Tonight the down sleeper is routed via Swindon, Chippenham and Westbury and waits at Exeter from 0337- 0412 and Plymouth from 0513-0550.
The route varies most nights depending where engineering work is taking place, sometimes it goes via Bristol, other times via Yeovil, but which-ever way it goes it will always be away from Plymouth (and usually Exeter) at the same time.
The timings are also quite generous, it has just passed Westbury 33 minutes early so will wait time at Taunton as well.
The up sleeper was 33 late away from Plymouth but only 2 late at Exeter due to the waiting time, this one also gets 33 minutes to get from Reading to Twyford, it only takes 6 minutes.