Is running it at 08:36 from Swindon enough time to turn round the unit what time dose it arrive from it's previous journey? What about crew when do they arrive at Swindon?
Arrives at 08:18 and I'm pretty sure it's the same crew on there up and down.
What about at Westbury does it stable or return from the platfom will it block other trains?
Slightly more complex. P1 occupied 09:28 to 09:32 (->WEY) ; P2 09:33 to 09:39 (-> WAT) and P3 09:35 to 09:38 (-> GMV). Previous trains cleared at 09:01 and next train doesn't arrive until 09:49. Currently the TransWilts train uses P3 - suspect it still could, with a shunt and that has a 14 minute allowance from arriving to being shunted. I think the WEY train may drop carriages, so sending the GMV through there may be an issue.
If all these are OK then it seems a very good move
Another reason, perhaps, for the :49 off
SWI» for this train is that it's close to a pattern - 08:49, 10:47, 12:47 and whilst clock face is good, I think the benefits of reaching Westbury for those connections outweigh sticking to what's already just a tendency to a pattern.