。
Is it okay if we make it for 10:30 am?
Literal
Promise [obj-を] am 10:30 [to-に] make-[even-ても] good [polite-Q-よろしいですか].
~てもよろしいですか is the politest variant of 'may I,' using よろしい (polite form of いい) and ですか. This is a formal business register, appropriate for scheduling calls with clients. 約束 here means 'appointment' rather than abstract 'promise' — context alone distinguishes the two senses.