We had a similar situation a few years back - we were stopping overnight in a hotel near LHR, then going to a wedding in London before flying out to HKG that night.

We wanted to check our bags and just have our hand luggage with us at the wedding. We were told that there was no problem checking in during the morning, but once we had checked our bags we shouldn't leave the airport.

Your situation is slightly different but the reality, as NickB has pointed out, is that the airline has no way of knowing where you go for the hours leading up to your departure.

Just as long as you present yourself at the gate at the appointed hour, everyone will be happy. ^


Nick