Casio mtg900 auto time update

You can download manual from Casio's web page. I give you couple links.

MTG900DA 8V Shock Shock Mens Tough Water Resistant Analog Digital Watches...

In depth Review of Casio MTG 900 Shock Waveceptor Tough Solar Watch

I am assuming you are reading the battery charge correctly. If so you need a new rechargable battery. Special battery so it is a little expensive. Make sure the person knows it is a "rechargable battery" you want. A regular battery will not work properly or recharge.

I have a watch which is solar type and the instructions say that several hours of sunlight will charge the battery but lamps need much longer (1 -2 days!), my watch now is left in a drawer.

If you haven't got instructions for your watch, to check what Casio recommend, you can get them on the net.

You can get instructions from the Casio web site.

Go to the casio web site "casio.com".

Select "support" and the "manuals",
watches;

Accept terms

Select "watch manual archive"

Read the number of the back of your watch and enter it into the search box

you can get
instructions from the Casio web site.

Go to the casio web site "casio.com".

Select "support" and the "manuals",
watches;

Accept terms

Select "watch manual archive"

Read the number of the back of your watch and enter it into the search box

Click on my profile (escapement), then click on Tips and Tricks. There you will find link to all CASIO watch manuals.Rate me, please

You can get instructions from the Casio web site.

Go to the casio web site "casio.com".

Select "support" and the "manuals", watches;

Accept terms

Select "watch manual archive"

Read the number of the back of your watch and enter it into the search box

Click on "search" and the download your instructions.

If you go to "world.casio.com" you will see the alternative languages available. Unfortunately Portuguese is not listed.

The MTG-900 supports automatic DST which can be activated in the time setting mode.  However, the ROM in the MTG-900 dates from before Congress (in their infinite ability to make mistakes) modified the DST schedule, so, instead of switching at the beginning of April and the end of October (as currently specified), it switches at the end of April and the beginning of October (as previously specified).
I do not believe that there is a way to change the DST scheduling or manually turn DST on or off.  I've resorted to changing the time zone manually and turning off the DST feature.  IOW, I set the timezone to Pacific (LAX) during PST, and, to Mountain (DEN) during PDT.

You don't need to set the watch back an hour.  You just need to turn off the automatic DST adjustment.
Hold ADJUST for several seconds.  Then, when DEN starts flashing (or whatever timezone you are set to), hit MODE The display will change to DST flashing at the top and on or auto flashing at the bottom. Click TIME/MEMO or RECEIVE to change on->auto->off.  Once off is flashing at the bottom, hit ADJUST twice and you will be out of DST mode and everything should be fine.

Did you go to Casio and download the manual? I just did after my battery change and I hoping it updates tonight at 2,3, or 5am with my watch in the window.