I've written tips before on spending non-wedding planning time with your fiance. I've also written tips on how a movie with a wedding in it can double as date night and wedding planning time because you can take mental notes on wedding ideas and inspiration. But here's another one:
Why not plan date nights at restaurants you're thinking of hosting your rehearsal dinner at? You can enjoy an evening out without talking about wedding planning but by the end of the meal you'll have a good idea if this restaurant would make a great location for your rehearsal dinner.
You can also have one or both sets of parents come with you to test out menus or plan night's out with friends and have them join in the fun!