I’m so glad you asked. So, I tested it. It took me 5 minutes, 12 seconds to get 52 weavercloth. Sorry the mobs were not so kind as to stop at exactly 50, so you’ll have to make do with 52.
At the same time I also picked up 12 weavercloth bolts, 7 duskweave, and 9 dawnweave. So 5 minutes for 80 total cloth. Or, 960 cloth/hour.