Mondays to Fridays the ticket is not valid until 09.00 or from when the Off-Peak Day ticket (if available on a particular journey) becomes available, whichever is earlier.
That's the old restriction, which confusingly is referred to still in a number of places. The new restriction is after 09:00 or any of the following trains:
08:35 Newton Abbot - Penzance
08:14 Plymouth ^ Penzance
08:40 Plymouth - Gunnislake
08:33 Liskeard - Looe
05:54 Exeter St Davids ^ Barnstaple
06:48 Exeter St Davids ^ Barnstaple
08:43 Barnstaple ^ Exeter ^ Exmouth
07:26 Exeter St Davids - Axminster
08:26 Exeter St Davids ^ Axminster
08:27 Swindon to Penzance
08:36 Taunton to Bristol Parkway
08:39 Patchway to Paignton
08:49 Hereford to Worcester Foregate Street (train continues to Birmingham New Street)
08:53 Weymouth to Gloucester
08:54 Swindon to Cheltenham Spa
08:50 Great Malvern to Westbury
That list itself is confusing because it refers to a train from Hereford, which is out of the rover area, and it is a London Midland service, and London Midland are not one of the operators included on the list of operators the ticket is valid on. Because
NRE‡ still has the old restriction listed I'd say you are fine on any train after 09:00, any of the listed trains and any journey where the
CDR▸ would be valid.