I'm trying to find how long one of my processes is running and ended up with few confusions.

/proc/uptime --> this is the time I power on the machine and not the time OS actually boots, is that correct?

ps aux | grep my_app
under START i get 08:45 , --> this time coincides with the time i powered on the machine, and not the time i actually started the app. any thoughts why that is so???

finally what is the best way to find how long my process has been running??

thanks in advance
david