A normal direct drive from Avignon to Bédoin takes from 30 to 38 minutes, depending on traffic and if you get lost. Try to avoid weekday rush hours - M-F - 7h30 to 9h00 and 17h00 to 18h30.
If you take the 17h51 train from Avignon TGV to CDG, I would not recommend you leave Bédoin - or the area around it - any later than 16h00. Even that might be pushing it for folks who are not familiar with the area/region/roads. Even at that time, traffic in Avignon will be heavy.
If you want to see the Monday market and then have a meander around Mt. Ventoux and perhaps some other gorgeous hilltop villages such as Crillon-le-Brave, Seguret, Le Barroux, etc., I'd plan to arrive for the market no later than 9h30 and I'd depart the market at 11h00 - head up Mt. Ventoux, then back down the other side at Malaucene. Then you have the choice of taking the route from Malaucene to Suzette to Beaumes-de-Venise, to Carpentras and then back down to Avignon - or Malaucene to Vaison, to Seguret to Carpentras and then back down to Avignon.
You could do all this in the 11h00 to 16h00 time frame. But there are SO many options here. These ideas are just a nice easy round.
If you want to stay in Bédoin for lunch, you could adapt this schedule to that too. Or you could pick up some fantastic picnic food in the market and stop at my favorite picnic spot on the route from Malaucene to Suzette (on the left with drop dead views - just two picnic tables which should not be too busy in Oct.).