I think a few changes in the handling of Rates would improve things.
1- Labor Rates shouldn't be an Inventory item, it feels like a work around and it's just not scalable that way.
2- Technicians shouldn't be seeing our costs for Labor Rates.
3- Some other unnamed PSA's handle this using a calculation, when the tech enters time they enter a work roll and a type. Such as, Server Administration ($120/hr) times After Hrs (1.5 multiplier) = 180/hr. Or maybe the multiplier gives a discount. It can also account for hourly minimums. Very powerful and the tech doesn't have to see the costs or even the rates.