Asking for more notice from management for visits to clients

There is a deeper problem than just "no notice." It appears that your boss is not managing the business and customer support very well. The business needs scheduling and structure to notify customers of upcoming upgrades, maintenance calls, etc.

The real question in front of you is: can you help him manage the business or is there anyone else in the business who could? For example, could you create a schedule of proposed client visits for the week and present that to him as a suggestion on Monday morning?

Not getting notice ahead of time is pretty common for travelling technicians, but the customer should always know ahead of time. That part of it is completely unacceptable.

I worked for 2 years as an "on-site" travelling computer and printer repair tech for one company nearly 2 decades ago. We had a dispatcher that would give us our assignments, but we often wouldn't get our assignments until either day of or as we were leaving another customer's location. If it makes any difference, it was considered a Value-Added Reseller (VAR).

Yes, it's pretty rough at times. You need to make sure you have fuel, cleaning supplies/whatever consumables you use, and know when to go back to the office to pick up parts.

But at the same time, if we were scheduled for cleaning a whole batch of printers, we would normally be told the night before, right before we left, so we would have some sort of expectation of the next day. We would also be told the day before for longer trips or for full or half day long visits.

It sounds like your boss is overwhelmed and understaffed, and more than a bit unorganized. They probably need to hire a dedicated dispatcher to handle all this communication between the business and the customer as well as you and any other service techs. You can suggest this to your boss, but don't be surprised if they react negatively. Too many businesses think they can't afford the "extra" person on payroll, except that this is one position that will absolutely pay for themselves. A dispatcher will help keep techs happier so you don't leave the company for a better job, and your customers don't leave for some place with better customer service.

Or the business thinks it'll take "too long" to hire and train someone, except that if the business continues, it'll be even worse when they realize it's not optional to hire someone.

But, again, you probably can't convince your boss. Generally, the best you can hope for is to put the idea in their head and let them come up with it months later "on their own." Or maybe you have an actually good boss and they take your advice. Who knows, but you.

Good luck and just remember that you can always leave. Businesses aren't loyal to their employees, so don't feel obligated to be loyal to them. Because if they need to fire someone, businesses generally don't hesitate to do that.