After Party Invitees

I don't know if some more details might help but you might add these into the comments here. What time is the reception and how long is it? Do you have vendors helping at this time or just people possibly supplying drinks and snacks? Is this just in the hotel rooms or in an additional rented area?

I think it could work fine if the reception is normal length, but it is hard to say who is ready to party so long after the reception. Most people would probably be happy just with the reception. You could be casual about who joins in on the party, or just have a polite send-away to them.

I think if people were privy to an after party they were not invited to, it might hurt feelings. So unless you can completely prevent anyone from finding out something else is going on (doesn't sound like it), I'd kind of let it be open invite, if it were me.

Your closest will obviously go, the people you're not as close to may not come because they are not close to you, or they may because they're having a good time at your wedding. Some people may not go because they're tired, etc. Honestly, the day of I'm not sure you'd care about who ends up at the after party, you'll be too busy having fun.