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.