Good grief DM!

I've just read this through and it seems to have got somewhat complicated along the way.

Just to confirm fkheng...

You have a map.
You know the start point of this bus and the end point.
You know the route in between.
You know how long it takes to make the trip.
You know the start time.

What you want to do is draw is how far the bus is along the route, based on the current time?

If you confirm/correct the above then you'll be pleased to know what I think you're trying to do is childishly simple...

On the other hand, if the above is completely wrong - I'll get my coat...