Maybe about 4 hours I'd say. Woke up at 3 and got through it by 6-7 AM playing straight through.
Really into the style. Seems pretty funny too.
Do you need to play the original to understand anything here?
No. There are some connections that make their way from the first to this but they aren't like fully followed upon.
Some characters in DG seem to be other family members not present in TT and that's about the long and short of it.