I hate being an a**hole but.... Have you tried the "search" feature? This question has been asked and answered 100000000 times. But I do hate when people just bitch and don't answer the question so I will say, from my experience searching the boards, about 4-6 weeks.

lolThis is a good question.
Prop is commonly used as a kick start to a longer ester cycle for most commonly 4 wks.
The mg to mg for the 2 esters if a bit different so try to sync that up to make a smooth transition.
Also what's your current pinning schedule ed or eod?
And whats the reason your changing esters now?
What esters are in the ultra test?
You are all ready ruing enanthate ester,no need to continue to runn the prop.
Drop the prop and continue with the enanthate there really is no need to run the ultra test,if your looking to get on a twice a wk pinning schedule just pin the enan solo no need to wait and run the prop the enan ester has built up enough you can drop the rest and run only enanthate.