It’s totally up to you, like everything with your wedding, there are no set rules!
The most common time, but by no means the only time, for a confetti photo is straight after the ceremony. For a confetti shot, you typically want all of your guests involved so it’s worth considering when everyone will naturally be together. So at the end of the ceremony when you walk back down the aisle or straight after the ceremony are a great times, or shortly before gathering everyone together for a group shot or for dinner. It's also worth bearing in mind that straight after your ceremony people will want to come, say an excited "Hello!" and give you a hug and congratulate you so we often find confetti shots end up being not quite straight after the ceremony but 10-15 minutes later once everyone has had a hug!
It’s worth talking your plans through with your wedding planner, wedding coordinator or your photographer - they’ll each have a wealth of experience to advise you on the best way of organising the shot.
It’s also worth bearing in mind venues may have strict rules on confetti, this may limit where it can be used or even ban it completely. Churches, for example, sometimes ask for it to be limited to a path often just outside the entrance and are sometimes have rules on the type of confetti you use - read on to find out more!