I would have been happy to let you use the money, if you would give me a date to leave.
Is this a past present tense? I need to explain this statement I made, correctly.
There is a tense problem in your original sentence
refers to something in the past. I would have given you the money, but I did not (because you did not give me a date).
refers to something that has not yet happened (you have not given me a date, I'm waiting for it)
The two parts cannot go together as they are, so either you put the dependent clause in the past:
or you put the independent clause in the future
The clause "I would have been happy to let you use the money" is an example of a Modal Perfect construction. You can see the modal 'would' and the perfective "have + -en".
The meaning is 'past + counterfactual' -- we use it to discuss something that was possible in the past but did not happen.
To combine it correctly with the second clause see the instruction from Nico. You need to adjust something to get at the meaning you want.
As far as I know the independent clause, "I would have XXX", is an example of the conditional perfect tense. If the XXX is been plus a gerund (ends with "ing") then this would be conditional perfect progressive tense. The second or dependent clause, "if you would XXX', is in conditional tense.