Hi Bubblepearl,
It will be best if you can give him a exact time, becoz on hot dates, he might take up other couples. For my wedding, I had my solemnisation at 7:45pm. He had another at 8:30pm in another hotel next to mine.
As for better timing, if you are going to have it at the wedding banquet, you can consider having it during your 1st march in. And most wedding banquets start late, you probably won't want guests to start strolling in during your solemnisation, so 8:30pm should be fine.