Personally I would leave around 10ish but then I am the kind of person who leaves everything to the last minute...
It is Bank Holiday so quite a few people will be travelling and although I think most would go on Friday, for the ones that can't for whatever reason, they will go Saturday.
For that reason, I would leave earlier than 10 (although I could never get out of bed for 6!) so that you miss the traffic.
The M6 (or whichever way you go) will be pretty busy at 10am on a saturday anyway, even more so with it being bank holiday weekend.