At the moment, the set that forms the Shrewsbury-Crewe local for the day spends the previous night at Shrewsbury, having arrived on the last Heart of Wales. The plan seems to be that this set will do an extra trip to llandrindod and back first every morning. The current first heart of wales departure which uses the 153 off the previous days Crewe-Shrewsbury locals which arrives from Crewe ecs in the early hours of the morning will now run slightly later (presumably the ECS will still run at the same time as it also contains the unit for the first Chester service from Shrewsbury, and the driver for the first Birmingham (which run at 0520 and 0518 respectively)).
That's correct.
Looking through Realtime trains, it would appear that the allocations for the HOWL are as follows:
1 set will operate:
04:45 Shrewsbury-Llandrindod
06:18 Llandrindod-Crewe
09:14 Crewe-Swansea
14:35 Swansea-Crewe
A second set will operate:
04:05 Crewe-Shrewsbury (ECS)
05:42 Shrewsbury-Cardiff
11:14 Cardiff-Llanelli
12:45 Llanelli-Cardiff
A third set will operate:
06:03 Swansea-Crewe
11:20, 13:15 and 15:22 Crewe-Shrewsbury
12:24, 14:24 and 16:24 Shrewsbury-Crewe
17:20 Crewe-Cardiff Central
A fourth set will operate:
07:16 Cardiff-Swansea
09:33 Swansea-Shrewsbury
14:05 Shrewsbury-Swansea
18:21 Swansea-Shrewsbury
And the final set will operate:
04:53 Carmarthen-Llandovery
06:42 Llandovery-Swansea
08:14 Swansea-Fishguard
09:54 Fishguard-Carmarthen
10:58 Carmarthen-Pembroke Dock
13:09 Pembroke Dock-Swansea
16:00 Swansea-Pembroke Dock
19:19 Pembroke Dock-Tenby
20:00 Tenby-Pembroke Dock
20:30 Pembroke Dock-Swansea
23:45 Swansea-Fishguard Harbour
01:50 Fishguard Harbour-Swansea
This set will then (it would appear) operate the 05:45 Swansea-Pembroke Dock and then return to Swansea, before making two return trips to Pembroke Dock, then a trip to Carmarthen before finishing in Cardiff.