As an example, if I am making plans to meet with a friend, and I say I am free on a specific date, say 2 weeks from now, and then I follow up by asking my friend "Or is that too far ahead?" To translate "Or is that too far ahead?" into Mandarin, can one say "会不会太久？“? Or is there a better translation?
It's pretty good.
Besides, I want to explain the difference between "太久" and "太迟".
"太久" means you spend long time. "太迟" means you spend long time and don't know whether something will what happen.
Your friend live the same city with you. You are going to visit him after two weeks.
you can say "我两个星期后来看你，会不会太久？";
Your friend has a trip in your city. You plan to meet him after two weeks. But you don't know when he will return home, you are afraid that he will have gone back home by the time you visit him.
You can say "我两个星期后来看你，会不会太迟？";
"太久" really means the period between a time and another one, the distance is too far for us to wait for. You can translate it as "It's a bit too late". Because when you hear this statement, usually means someone is not much patient to wait for others, maybe come with some complaining.
For "is that too far ahead", it should be “太旧*之后*”, For "too long (PERIOD)", it should be ‘太久’.