How long do you give people to decide if they want to be apart of your Bp?

My FH and I live in a different state from both our families and long time friends so many are going to be flying. I have my sister that feels she will be able to make it, but it's still on the fence. My FH has a friend who said he'd try. I'm wondering how long we should really give them before we ask others to be apart of our bridal party?