I think this should be 你有时间在做吧。(再 replaced with 在), shouldn't it?

I'm not a native speaker but I'm quite sure the sentence is right as it is now. I think this sentence is based on the same pattern as

看情况再说 = (it will depends on the situation , lit: first see the situation, then talk about it again)
To my understanding this pattern (something 再 verb [吧]) means that the one(s) you're talking to (or yourself) were about to do "verb", but eventually find it's not the appropriate time and prefer to wait for the "something" before doing it.

On the otherside I don't see any logical reason to have 在, as the main way to use beofre a verb is to describe something which is happening now (more or less the english be +ing form), which is not the case here, as we're talking about a future action

Once again I'm not a native, so maybe we'd rather 等一个中国人来解释一下再说 :P

Ah, I guessed something like this: I thought 有时间 would be indicating future and 在做 would be used to convey the -ing meaning, in total being "in the future, you will be doing". But I guess this doesn't exist (or is expressed using a different structure). Thanks for the explanation!