Won,t start after sitting for a short time, but will start fine when cold

Josh, Code 55 for your Altima simply means no faults were found/no malfunction. Do you mean car would not crank(engine not turning over) or did you mean engine will crank, but not start. I will post troubleshooting links to both conditions below. If not comfortable, have a good Technician look at it, diagnose and estimate repair.
Why Your Altima or Sentra Won Start How to Fix it
How to Troubleshoot No Start Nissan 2 4L 2 5L
http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=1215302
Why car won start troubleshooting tips

By chance did you check your oil level. That would be ideal before your engine blows out. If that is fine, more in likely it maybe normal. Some GM vehicles do that also due to the cold weather. After sitting for a long period of time the oil will settle in the oil pan til you crank up. The knocking noise may last for 5-10 sec then it stops because the oil is lubricating the pistons again. But if it is constant and oil level is good, get a mechanic to check it out. Hope this helps.

It may have to do w that timing chain due to vacuum advance being off too.

may be you should make a diagnostic and you can do it in a garage or you can do it by yourself if you want to do it by yourself you need some tools and you can find some good ones here: diyobd2.fr

is the air filter clean?

It is probably the "cold start" cycle. A Temperature sensor will send a signal to the computer in order to make the fuel charge rich and change the timing. This will last less than 3 minutes on many cars.

The process is similar to the old "choke" system adding a timing change to the rich fuel mix. Many cars have 2 Temperature sensors and for those you want to change the one that does NOT work the dash gauge or light. The sensor you want is dedicated to providing temperature info to the computer.

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sounds like you need to take to shop and let someone that knows what to do fix it not you

Then you have a start up problem and it reside with the cold start valve,The cold start valve operates even if the vehicle is warmed up,the cold start valve can be plugged up,or even have a bad connection,The cold start valve operates by a thermotime switch.This switch located on the near bottom of the radiator may have gone bad or disconnected,Here is the easy cost effective route, replace them both,it will cost more to trouble shoot it than just replace it.

check fuseable link near battery if it's blown would pay to look for short circuit before doing much more

what car is it ,it could be a cold start sensor/ coolant sensor