Michael,
Of course, it matters. Of the various options, one of them will be the most appropriate, and the others may be slightly sort of appropriate or could just be mistakes. In your second paragraph you are confusing duration with work. Let's say the 100 hours
of work was one full time person assigned for a duration of 100 hours. That's 12.5 8 hour days, or 2.5 weeks, on the standard calendar.
After you logged say the first Monday - Friday that was 5 days of duration and 40 hours of work.
Then the task was interrupted by something the client did which took 20 hours of duration.
Split your task into two tasks, A1 and A2, the first one with duration 40 hours and work of 40 hours, and mark it complete.
The second task is 60 hours of duration and 60 hours of work.
Make a task for whatever the client did. Call it B, 20 hours duration, zero work.
The your A1 is predecessor of B, and B is predecessor of A2.
Simple. The overall duration of the three tasks is 120 hours, but the sum of the durations and work of your tasks has not changed.
Any help.