I'd say that's about right - tho never been to Copt Howe. Timewise from the M6 I'd (very much a guess!!!) say the 'road time' (not including time at sites) would be 3 hours give or take.

If you use that loop & have a (fair) bit of time left, you could just mebbe do Druid's Circle of Ulverston at the end.

love

Moth