@Daniel9481 Message the guest now and tell them (not with the long explanation above) that you have a technician coming to repair the dryer on the 6th. Say that you hope it will not be an inconvenience, but if it is, you will happily reschedule the repair. If they say it would be an inconvenience, you will need to reschedule. Chances are they will say it won't because they'll probably be out anyway, but it's important to pin this down now. Tell them also that as soon as you know the arrival window you'll let them know, and assure them that you (or someone) will be there with the tech to make sure they're disturbed as little as possible.
I just had this situation today (with a washing machine), and I was relieved the guest was agreeable, because it's absolutely brutal trying to get things taken care of at my listing in Maine this season, as I imagine it is for you in Newburyport!