Probably just a bug.
At first I thought this was that the time was accelerated or something so you can complete it in like 2 minutes or something..
I had it paused for long perioids too and actually I had that same thoughtI just did 9hr Tsukuba earlier this week also and noticed this. I thought maybe it had something to do with clock drift in the counter since I left it paused for long periods of time over the span of about 3 days until it was done.