Yes, mason bees don't require a lot of attention in comparison to honey beekeeping. Effectively the ones involved in fruit tree pollination are only active for around ten weeks. So winter time is a relaxed time - counting cocoons, preparing more blocks, paper tubes and collecting dried plant reeds which can be done in spare time. There are however also those who extend the solitary season by encouraging leaf-cutter bees which last into the summer, and observe ground bees and smaller bees that come later in the summer (if you are that way inclined). The latter can also be 'accommodated' with specific artificial habitats - although I have yet to accomplish this.
As I have several bee species in my Picardie backyard/garden, I will certainly be hopping around filming them throughout the summer. Perhaps your husband may want to film his bees, and post them online (here?)... or check out my 30 videos ion YTube on my 'solitarybee' channel.
Although all things considered, perhaps you shouldn't tell him about this - these are fascinating critters to hunt down and we wouldn't want his increased enthusiasm for solitary bees becoming a problem for you