is there a time such as every 10 mins it's refreshes?
There may be a set time, actually, but I don't know what it is.
I have characters who at this point never leave their ships. I might log in, check my UT, and see there is no UWM missions available at the level I want. I do my thing, do some crafting, check again 5-10 minutes later--boom, there's a mission there.
I do not leave my ship, as the other commenter said is necessary, or go through any kind of loading screen.
It's not universal. Sometimes I check back and there is still no mission there, but it happens often enough that I can advise "wait a bit, and try again".