Both Al and Mike are correct; you should use one of these forms:
a Would it be OK if I confirmed around 3pm?
b Will it be OK if I confirm around 3pm?
Use (a) if you're in a situation where you're seeking the person's permission: that is, you need permission to either be able to confirm later, or permission to confirm later at the time you mention. With the (a) form, you're seeking the other person's input or approval, and their decision might completely alter your plans.
Use (b) if it's already established that the plans are agreed, and now you're working out logistics. You're already agreed to do whatever it is, and you've agreed that you can cofirm later, but now you're seeking to find out what the best time is for confirmation.
This is a subtle, idiomatic distinction more than one of syntax.
From a syntactic point of view, I believe, 'would' is a modal auxiliary verb, indicating possibility not certainty; whereas the auxiliary verb 'will' conveys definite intent of action.
Best Answer
Both are acceptable, but the usage is slightly different. The following extensions to the sentence illustrate the most common usage:
In general, would is used in situations hypothetical, or contingent on some unfulfilled condition; will is used in situations that are more certain. The first sentence takes will because the speaker definitely intends to take the monitor back. The second uses will because, although there is a condition, there is a definite possibility of it being fulfilled. The third sentence takes would because the speaker has no intention of taking it backāand therefore the condition is entirely hypothetical.