Here is the timetable from December 2008 for trains Worcester - Gloucester (from NRE^▸ (National Rail Enquiries))

Trains leave from Worcester Shrub Hill for Ashchurch, Cheltenham & Gloucester at:

GW^» (Great Western - used as an abbreviation for the area / lines under the Great Western franchise, as opposed to FGW which includes "First", the company operating them too. For tickets - about): 7:09, 9:00, 11:08, 13:07, 15:07, 17:07, 19:05, 21:09, 22:32
LM^▸ (London Midland - recent franchise): 9:56, 12:15, 14:13, 16:01, 18:14, 20:05f

Trains leave from Gloucester for Cheltenham, Ashchurch & Worcester Shrub Hill at:

GW: 6:01, 7:15, 9:38, 11:36, 13:38, 15:37, 17:38, 19:38, 21:34
LM: 09:10?, 11:13, 13:16, 15:13, 17:10, 19:10f, 21:10?

Key:
GW = First Great Western, most trains start from/terminate at Great Malvern
LM = London Midland
f = train starts from/continues to Worcester Foregate Street
? = Train not listed in online timetable however 6 trains in each direction would mean a train departing at one of these times

Correct at 17th September 2008 - may not be the final timetable released

Southbound timings fill the gap, but northbound services are not very far apart?