A one-act play might be reasonable length, although they can go 20-40 pages. But if you read one-act plays, you'll find conventions of short drama, which is all you have time to write. Try to read contemporary, even young-adult drama, so you have familiar subject matter. You might check out the current drama at Quirk-Sponberg Theatre:Dead Man's Cell Phone. But set reasonable goals, so you don't get discouraged.