Here are the Pompeii opening times
Opening Times
November - March, every day from 8.30 a.m. to 5 p.m. (last admission 3.30 p.m.)
April - October, every day from 8.30 a.m. to 7.30 p.m. (last admission 6 p.m.)
Closed: 1st May

Pompeii Ticket prices (as of February 2010) are as follows:-
Single ticket - valid for 1 day
Full price: € 11.00
Half price: € 5.50 (*)

MULTI SITE TICKET
access to 5 sites: Herculaneum, Pompeii, Oplontis, Stabiae, Boscoreale) - valid for 3 days
Full price: € 20.00
Half price : € 10.00 (*)

Free of charge: for EU citizens under 18 or over 65 years old.

(*) Reductions: for EU citizens aged 18-24 and EU permanent school teachers.
Reductions and free tickets can be issued only by showing a valid document (passport, identity card, driving license).

Excursions from Rome are offered by the Big tour agencies, most of which have offices around the Termini Train station. We have not personally taken one, so cannot offer a specific recommendation. You travel by 50 seater bus and tours are most often run in multiple languages. Departing around 7am plan to return to Rome no earlier than 7pm.

Another option would be for you to catch the high speed train from Roma Termini (main station in Rome) and then meeting your guide either at Naples train station, or at the site of Pompeii. This would allow you to have more control over the guide, since you can book directly with a guide. Many have their own sites these days.