How to test my program?

I'm already done my C# server and i need to do 3 test:

1. How it working on different operation systems (windows 7, 8, 10) and architectures (x86, x64).
2. Stress test like every 20 seconds update some data and see how server react on it and research how much memory eat.
3. 24/7 test, it's like how my server working in normal regime in long period.

I definetely should done first test, it's necessary. But should i do a stress test, and 24/7 test on every OS and architecture or it will be enough to pick some and test only on it ? Cause i don't have so much time for it.