I've got the route pretty much sorted now and it's about 230 miles. Assuming we leave as planned at 9am, coffee stop will be about 10.30am and lunch about 1pm ish. Just depends on traffic and how often I take the wrong turning. Should be back in Exeter before 5pm.
Meeting point for the start is Wickes car park on Eagle Way, Sowton Ind Est, Exeter. The services at J30 gets horrendously busy so this is just 200 yards past it, and we're heading off in that direction anyway.
I've done the route in MyRouteApp but not sure I can share it if you haven't got an account. Happy to make the route public so you can download it to your device.
Anyone wanting to join midway let me know where you're thinking and I'll give you a rough ETA, but don't want to be hanging around for ages as it's a long enough day as it is