Basically you don't spray while the trees are in bloom and the bees are around. You can spray up until the buds get pink tips, then again just after petal fall.

Really depends what you are spraying for as to when and how frequently. I have apple scab issues, so I'm best to spray with a fungicide when the leaves first show, maybe again just before bloom (pink tip), then again after petal drop, maybe again 10 days after that. Technically I should probably continue spraying every 10-14 days into August, but with scab it is the initial spring infection that can destroy a crop, secondary infections once summer has set in cause very little problem so you really only need to spray for that if you want all of your apples to be perfect.

Apple maggot or other insects are a different matter. I've never had problems with those so don't spray for them and can't really offer any advice there.

I agree that it depends where you are, but equally, it should depend on what you see. i manage about a hundred orchards in about a 140 mile range north of NYC and have learned i can get sound apples with usually only two sprays all season. Been doing this for 25 years here.

You will need to mix two materials- Triazide and Immunox and apply once at petal fall and again 10-14 days later and if apple fly maggots don't show up that may well be all you need all season.

It is very bad advice to suggest spraying every two weeks with no idea about what you are gunning for. Your vendor shouldn't be dispensing advice on managing fruit trees, IMO.