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.
"Would" suggests conditions necessary for a state to occur or an action to be performed.
This code would need to be modified given this requirement.
"Will" may be used in the same manner. (acknowledgment to Barrie England for this point)
This code will need to be modified given this requirement.
"Will" is also used to express a determined future outcome.
This code will have to be modified to satisfy upcoming requirements.
Best Answer
The three sentences below demonstrate correct use of would/will in your situation: