4 weeks?!  Zounds!  Even rehearsing every night, I don't see how your actors will have time to get off book in two weeks if they are in rehearsal 5 nights a week.  Earnest has such a small cast, it's hard to call them in for rehearsal in segments.  About the only one with a little bit of freedom is Lady Bracknell, who is only one in Act I and the end of Act III. 

Whatever you do, get your read through done the first night (or skip it all together), and get your blocking done by the middle of the second week--no later. 

Even though this is CT and the members are here for bonding with one another as well as acting, you'll need to stress the importance of working on lines, blocking, and character development when they are in the rehearsal but not working with you for the moment.

As a director, you need to be entirely prepared for every rehearsal.  If you haven't pre-blocked your scenes, you want to get those done now in your book, so you only have to dictate the movements and walk through them in the actual rehearsals.

Lastly, start each and every rehearsal ON TIME--even if only 1 actor is there.  Make the other actors stay late to make-up what they missed.

Have a good show!  Earnest is one of my all-time favorite plays!