Yes I know they can't give exact times - but if you're the first appointment they could say that
The system that allocates work doesn't 100% know who gets what and where until the very last minute, so although it might be pondering giving engineer X task Y first thing tomorrow, maybe it finds a task more suitable, or a total care task drops in that takes priority. Maybe engineer Z rings in sick, or his van breaks down, so then X has to go cover his task instead. It really is quite a lottery.