I note that this was posted sometime ago so I hope your production went well

I would be fascinated to hear what happened and how it went down...
I directed this in 2000 when i lived down south...
We used a very simple setting in the loft of a church (a wonderful but tiny acting area)... with just three tables and a folding flat to indicate doorways/walls
I followed casting and kept the waiters/owner as one actor... I don't know if it would work any other way.
As for the the time shifting... I did not worry about it... the only physical clues I used were the costume changes that was it... and those are obviously required anyway.
If you read the play you will see Sir Alan throws in a ton of clues for the audience.... I honestly never saw it as an issue although everyone who reads it THINKS it's going to cause a big problem... i had many actor's asking me how I was going to let the audience know.... my answer was the play tells them so I don't need to....
I spoke to many of our audience and they said that after the 2nd or so switch they understood 100%... in fact my explanation of the idea in the director's notes confused them far more than the play ever did! My approach seemed to do the trick as we were awarded with many plaudits for it in the local Drama Federation.
I do love this play as it is one of Ayckbourn's best (mind you I love 99% of his stuff). The balance between the broad humour and the desparate darkness in this play is superb. I hope you had your audinece laughing and crying in equal measure!