Unfortunately, once you send a photo-sharing request to your friends, they will receive a push notification instantly, which cannot be cancelled. Otherwise, it may confuse the receivers.
However, after the receiver accepted your request, you could change the photo-sharing status as follows:
- Go to in the bottom menu
- Tap your friend's name
- Tap your friend's avatar icon
- Scroll down to Photo Sharing
- Tap Active to change the status