The only planned weekday Castle HST services from December 11th are to be:
0638 Plymouth - Penzance
1015 Plymouth - Penzance
1042 Plymouth - Penzance
1142 Plymouth - Penzance
1547 Plymouth - Penzance
1555 Plymouth - Penzance (yes, that's correct, eight minutes after)
0850 Penzance - Plymouth
1250 Penzance - Plymouth
1315 Penzance - Plymouth
1350 Penzance - Plymouth
1815 Penzance - Exeter St David's
1850 Penzance - Plymouth
I have these diagrams:
Monday to Friday
5C02 0606 Laira - Plymouth ECS
2C02 0638 Plymouth - Penzance
2P08 0850 Penzance - Plymouth
2C68 1142 Plymouth - Penzance
2P17 1350 Penzance - Plymouth
2C31 1555 Plymouth - Penzance
2P27 1850 Penzance - Plymouth
5P27 2109 Plymouth - Laira ECS
5C11 0945 Laira - Plymouth ECS
2C11 1015 Plymouth - Penzance
2P15 1250 Penzance - Plymouth
5P15 1453 Plymouth - Laira ECS
5C65 1002 Laira - Plymouth ECS
2C65 1042 Plymouth - Penzance
2P16 1315 Penzance - Plymouth
2C29 1547 Plymouth - Penzance
2E26 1815 Penzance - Exeter St David's
5P26 2145 Exeter St David's - Laira ECS
Saturdays
5C40 0430 Laira - Plymouth ECS
2C40 0515 Plymouth - Penzance
2P10 0740 Penzance - Plymouth
2C16 1015 Plymouth - Penzance
2P90 1315 Penzance - Plymouth
2C28 1640 Plymouth - Penzance
2P95 1930 Penzance - Plymouth
5P95 2145 Plymouth - Laira ECS
3C12 0525 Laira - Exeter St David's ECS
2C12 0722 Exeter St David's - Penzance
2P86 1113 Penznace - Plymouth
2C22 1343 Plymouth - Penzance
2P26 1548 Penzance - Plymouth
5P26 1757 Plymouth - Laira ECS
5C20 1159 Laira - Plymouth ECS
2C20 1243 Plymouth - Penzance
2P24 1515 Penzance - Plymouth
5P24 1731 Plymouth - Laira ECS
1555 Plymouth - Penzance (yes, that's correct, eight minutes after)
The 1555 calls at more stations, so despite leaving only 8 mins later it arrives in Penzance a full 30 mins later - by Truro the 1555 regains a the usual off-peak half-hourly pattern offset from the 1547.