I am trying to create a time - distance plot of a series of trains in a
timetable. Each train will be represented as a continuous diagonal line from
start to finish. The stations are represented by a number giving their
mileage away from the start position. The times are represented in the hhmm
format of the 24hr clock, e.g. 1830 for half past six in the evening.

Couple of problems here...

Firstly, Excel doesn't like the time format with no colon, even if I'm using
a custom format of hhmm. At the moment the times are displayed with a colon
which means the times take a lot longer to enter. Any ideas to force Excel
to accept hhmm?

Secondly, where a train does not stop at a particular station but runs
through non stop, there is no time coordinate for it on the timetable and
consequently no data point on the graph, hence this results in a gap in the
diagonal line until the next time the train stops. Any ideas for making this
line continuous without entering a time, e.g. a line drawn between the two
times the train stops over two or more data points, instead of
line-gap-line?

Any ideas?