Learn Finnish: Käykö aamupäivä teille hyvin? - Does the morning suit you well?

This is due to the verb käydä. When käydä means "to suit" or "to be okay for someone," it requires the experiencer (the person it suits) to be in the allative case, which is the -lle ending. Therefore, "suits you" translates to käy teille.

Could I use the verb sopia in this sentence instead?

Yes, absolutely! You could ask Sopiiko aamupäivä teille hyvin? meaning exactly the same thing. Both käydä and sopia govern the allative case. Käydä is very common in everyday spoken Finnish when scheduling things, whereas sopia is slightly more neutral and works well in any context.

What is the difference between aamu and aamupäivä?

Aamu refers to the early morning, roughly from when you wake up until 9:00 AM. Aamupäivä literally means "morning-day" (forenoon) and covers the later part of the morning, usually from around 9:00 AM until noon. When scheduling meetings, appointments, or visits, aamupäivä is usually the more practical and common term to use.

Why is the question particle -kö attached to the verb käy rather than another word?