What's the shortest time?
What's the longest time?
What's the needed resolution, ie will there be times that are 345us or is 200, 300, 400, that sort of thing enough?
What kind of error can you accept?
How many "channels"?
Since you're talking microseconds it's either going to get "in the ballpark" or very very tricky if you need precision on many "channels".
Do you have a PIC this needs to run and if so which one and at what Clock frequency is it runing? Or can you select the most optimal PIC for the task?

I'm not pretending I have an ready to go answer but it's of no use to either of us describing possible solutions which clearly won't work once we know the details.

So, more details are needed.

/Henrik.