I baught a 3-outlet timer yardstake #15137. why does it blink on all settings except the on at all times?

It is a very basic mechanical timer. I have 3 of them.

Remove it from the wall.
Pull the tabs up for Off and Push tabs down for On.
Set the Time by turning the dial, time to arrow.
Set the slide switch to Timer On.
Plug in the appliance.
Plug the timer into the wall socket.

Manual and Advertising is here.

GE 15119 Manual - Waterheatertimer.org

http://waterheatertimer.org > pdf > GE15119-Man...

PDF GE 15119 timer manual http://waterheatertimer.org/How-to-set-timers.html http://waterheatertimer.org/GE-timers-and-manuals.html#52012.

GE 15119 Indoor 24-Hour One-Outlet Plug-in Basic Timer ...

https://www.toolboxsupply.com > products > ge-15119...

GE Indoor 24-Hour Mechanical Timer is an easy-to-use basic timer. Ideal for lamps, seasonal lights and portable fans. Turns a lamp on/off at desired times daily, ...

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Usually a wall timer is single channel ... even if it has two outlets... so there is only one program that controls the timing.
If you want two separate circuits, then you need a 2-channel timer... they used to offer some 2-channel models but I cannot find them any more.

Alternative would be two timers.
Or two bar timers will fit on same outlet (except bar timers are usually 24 hour and not 7-day)
http://waterheatertimer.org/Woods-timers-and-manuals.html#bar

Woods timers and manuals

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

I don't have repair for defective timer.
If following information does not apply to your timer, then add a comment with clear description of timer for possible help.
http://waterheatertimer.org/pdf/Woods-59403.pdf
http://waterheatertimer.org/pdf/GE-15117-Manual.pdf
http://waterheatertimer.org/Woods-timers-and-manuals.html#6-24

1) The only complaint about this 6-button timer sold by Woods, GE and Westek is the MODE doesn't work.
The key to this timer is to finish programming, and then press Clock to return to current time, and at this point the timer is in correct mode.
Then do NOT press mode button ever for any reason, except to reset timer.

2) Try resetting timer by pressing Clock Mode and Prog buttons at same time, and then re-program timer.

3) Timer is not heavy-duty. Load rating is 1000watts incandescent, and 1/4 HP.
If load rating is greater, then timer will not operate as expected.

4) If you have problem with timers, try timer on different load and on different outlet.
Test outlet for polarity using circuit analyzer.
http://waterheatertimer.org/How-to-wire-Cooper-277-pilot-light-switch.html#circuit-analyzer

I do not have repair for defective timer.
Most timers have limited 1 year warranty, except some Intermatic timers that have limited lifetime warranty.
Last step troubleshoot for timer is to reset and reprogram.
Timex Easy set is reset by pushing down Hour and Minute button same time.
If functionality is not restored, then buy another timer.
If timers fail frequently, then test outlet with circuit analyzer. And read load rating, try timer on different load, for example high wattage loads will shorten life of timer, and not all timers are made to control every type of load. Buy appliance timer for air conditioner or toaster oven.
http://waterheatertimer.org/Woods-timers-and-manuals.html#Timex

Most time-all timers have two different trippers on dial.
Push down and rotate tripper to desired ON time and OFF time.
Then manually rotate dial until current time lines up with a mark or arrowhead.

To replace timer with new one:
Buy TN311c with 3 sets of on-off trippers that push onto dial, and 3-prong outlet.
http://www.amazon.com/Intermatic-TN311C-Heavy-Grounded-Timer/dp/B00002N5FO

Buy TN111c with 2 sets of on-off trippers, and 2-prong outlet
http://www.amazon.com/Intermatic-Appliance-Security-TN111C70-Settings/dp/B00002N5FI/ref=pd_cp_hi_3

For digital timer:
1) Timer is defective
2) Conflicting programming so timer does not perform as expected
3) Timer not set to correct mode.
4) Program 'off' is set correctly, but program 'on' is not set or 'on' time conflicts with other programming.
5) Current time not set correctly
6) Polarity on outlet is reversed or noise on the line. Check outlet with circuit analyzer.
7) Combination of factors listed above
http://waterheatertimer.org/Woods-timers-and-manuals.html#Oval

Try moving time back to 7:30 and see if that works.

You posted under dual analog timer.
You can experiment with analog timer by manually rotating the dials using fingers. Unplug all yellow daytime outlets, but but leave blue nighttime outlets plugged-in and then rotate dial.
Try same thing with digital, except you have to wait for hours to pass.

Line noise can affect electronic timers. Use cheap circuit analyzer from home center to check outlets.
Try different load on blue outlets and then yellow outlets to see if specific fan-light-motor is causing problems for timer.
It is also possible that timer is defective.
After discovering exactly what problem is, add a comment here so your work will carry forward to others with same-similar question.

For folks wanting to see zilla timers with manuals and images:
http://waterheatertimer.org/GE-timers-and-manuals.html#zilla

Add a comment for more free help

Also take advantage of fixya expert assistance live.
For a price, expert works with you while you work on timer or any do-it-yourself project.
Fixya is always less expensive than a service call.

temp setting
1. press the temp/timer button untill the temp icon blinks
2 use up and down arrows to set temp.3 the temperture icon will stop blinking and the current room temperture will appear after desired temp. is set.
4 the heat will turn off shortly after the desiredtemp. is reached and the temp. ndisplay will blink.
5 the heater will turn back on when room temperture drops below the set temp.

timer : auto -off press the temp/time button untill timer icon blinks. the hour display will apear. the auto off icon will also appear.

2. use up and down arrow buttons to set the heater operation time between 1 and 10 hours. this function will activate once the timer icon stops blinking.
3. the heater will automaticly turn off when time runs out.

set temperture first so heater will cycle on and off till shut down time reached

Hello I made a couple of videos showing how to first set the time and day and then how to program this Westinghouse model 28499 3 outlet photocell timer.

Put black tape over photo electric eye and see if lights stay on without blinking.

Dusk-type yard stake has photo electric eye, which is visible as round glass ball.
Lights from circuit can cause photo-eye to think it is daylight, so circuit turns OFF.
Moment later, photo-eye thinks it's dark and lights click back ON

Usually 6-outlet yard stakes have 4 top outlets controlled by timer.
Normally bottom 2 outlets are ON full time.
Make sure bottom outlets are not blinking also, which implies problem with outdoor circuit or basic timer problem.
Check circuit with inexpensive circuit analyzer from Home Depot electric department.

Photoelectric eyes go bad easily, but usually they don't blink.
They stick ON or OFF.