Hi Dee,
I used to organise coach trips regularly from my home town in Bucks just north of London. We often crossed the Channel, usually to Calais but sometimes we did the Adinkirk and Bruges trips. Those were booze cruises but we went for the day trip. The driving time from Calais is about an hour and twenty minutes as Mr Veritas says.
I empathise with the start time as we had to meet the coach at 06.50am. You then stop for a driver break at Thurrock Services before continuing on to Dover for the ferry. It's fun at first but the trips become a real drag after a while. You board the coach feeling rotten after about three hours sleep then you try to snooze down the motorway but can't because the coach seats are really uncomfortable and someone behind won't stop yakking about some inane rubbish. The ferry trip is enjoyable though and we always spent the crossing on deck.
I hope you have a good time. You should get home about 7.30 and then you'll sleep like a log that night. It's a good day out and Bruges is beautiful. Lots of canals, chocolate and lace. Have fun.