181>280 quest points

How long will this take, in terms of total hours?

I'm thinking ~40 quests at about 45 minutes for average so ~ 4, 5 days of solid questing?

 

Depends if you have done the quests before on another account.

Your estimate should be about right, but if you have done the quests before it is faster obviously since you know what to do (since guides aren't THAT specific sometimes).