Availability of same-day or no-reservation hotels & lodgings around Hokkaido late September?

Hi there, I’m planning a 5-6 day motorcycle road trip around Hokkaido, with a general itinerary of Chitose > Wakkanai > Teshikaga > Lake Akan > Asahikawa > Chitose. The challenge is that I’m planning on riding 4-6 hours a day, but I’m not too sure how much ground I could cover depending on local roadside attractions / road conditions. 

I plan on getting a local SIM to make local calls. If I were to call around 3-5PM, would most hotels be generally receptive to same-day bookings? I’m trying to avoid situations where I have a booking, but won’t be able to arrive before dark, or I arrive too early and could easily ride into the next major town along the route. 

Thanks!

EDIT: Will be arriving after Silver week (21st-23rd)