1. the first one can occur, if they can't be on time they will ask if they can arrive later and as the host you get to decide whether they should still come or not, either way the guest will arrive on the pre-determined time
2. if the start time is flexible, this is stated clearly as part of the invitation e.g. you invite people for a bbq "starting around" 2PM (rather than at 2PM) and make it clear that they can arrive and leave at any point in the afternoon, just that they should not arrive before 2PM
1. the first one can occur, if they can't be on time they will ask if they can arrive later and as the host you get to decide whether they should still come or not, either way the guest will arrive on the pre-determined time
2. if the start time is flexible, this is stated clearly as part of the invitation e.g. you invite people for a bbq "starting around" 2PM (rather than at 2PM) and make it clear that they can arrive and leave at any point in the afternoon, just that they should not arrive before 2PM