This is a common gripe with any home delivery service, but if you think about it, if it was possible to work around a two-hour window, all firms would, because it wouls make them much more popular with their customers.
The 'before one' type system has evolved after long experience - based on the problems that can occur with making times any more restrctive, so yes it is really annoying, but if it could be done better, it would!
Just remember to save your temper for the people who mae the appointment, not the ppor eningeer who is already having a bad day, which is going to get worse - if he's late for you, he'll be late for all his afternoon appointments as well. Give him, and yourself, a nice cold drink, and take it easy, then ring up and make your feelings known to the powers-that-be.