To prevent forgetting a PS check your itinerary first thing in the AM. Block the time before that out so you get where you need to be on time. If you are running late and it is an early seating they will most likely be able to get you in, but you may have to wait a bit. If you are running more than 10-15 minutes late they will not hold your PS and you will need to go as stand by, if they can fit you in. Your best bet would be to call and see if they can reassign you another, later PS. If you know you won't make your PS that frees up the "anticipated table" for someone else when you call.