Q: When should you change your ukulele's strings?
A: When you won't need to play it for 10 days!
It's been said that all jokes have a basis in fact. This one is no exception. New strings can stretch for up to 10 days. You'll find yourself retuning almost every time you pick up the instrument (and sometimes while you're still holding the instrument) until the strings settle in. This is NOT due to a fault in the strings or the instrument. It's the way new strings behave.
For soprano ukuleles, I have found that tugging on the strings before I tighten them helps them settle in a LOT faster, BUT
- Don't overdo. The ideal is to have about two winds on the peg once the strings have settled in and
- Do NOT tug on the 3rd string (the thickest one). Make it as snug as you can without raising its pitch before tightening.
That part about going to bed is another way of saying let the uke sit for a bit. I've used this technique to restring a uke in the morning and take it to a jam in the late afternoon. Eventually, you should be able to, too, but see (1) above. Don't press too hard the first few times you try this. With practice, you'll figure out the right amount of tugging needed.
Something like this technique may work for concert and tenor ukes, but I have no real experience with them except for the occasional concert uke. So, I'm afraid you're on your own here.