Swindon to Dartmoor... on a Friday?

[Pulse]

I'm looking at taking a quick 2-day trip to Dartmoor, from Swindon. I'd love views of others on my options:

1. Leave work early (midday, perhaps) on the Friday.
2. Leave at peak time on the Friday. This surely would be a nightmare.
3. Leave at whatever a sensible time is to avoid traffic on the Friday (6-7pm, hitting the M4/M5 interchange at 7-8pm).
4. Leave early on Saturday morning (around 6am).

I am keen to get 2 full days there, but even leaving early on the Saturday allows me to do that. Any views?

[Pulse]

Saleen and Hopey, would I still be worth doing that if going on the Saturday morning? Would be a more interesting drive than the motorway either way.

I've decided to go on Saturday morning instead. It's not that long of a drive, and avoids another night in a hostel. Man maths means I can spend this money on petrol.