When you have your initial appointment where the implants are inserted, you may be without teeth for a week or so - all depends on your dentist.
When I had mine done, I had a denture consisting of 2 teeth, which I was not allowed to wear for a week, whilst the stitches healed (I locked myself in the house for a week and when I went out I wore a scarf .... luckily it was Feb so I got away with it).
When I had the stitches out, the dentist trimmed my denture back, to prevent it making contact with the gums where the implants had been inserted. I was told this beforehand and I thought that the gap between the denture and gums would have been visible, but it was hardly noticeable.
In theory, your denture should fit after the surgery, but nothing is guaranteed.
Best to talk to your dentist, as I suppose it'll all depend on what route he follows.