Here's the last in my series of journey time comparisons across Wiltshire.

Direct train:
06:15 Swindon -> 07:36 Salisbury
(the fastest public transport by far - but if you miss the 06:15, the next one is at 18:44)

Typical daytime train:
12:30 Swindon -> 12:59 Bath
13:23 Bath -> 14:28 Salisbury
(some services may be up to 15 minutes quicker, with shorter connections at Bath)

Suggested bus route:
13:12 Swindon -> 13:56 Devizes
14:15 Devizes -> 15:15 Salisbury

By bus following the railway route :
10:50 Swindon -> 11:49 Chippenham
12:00 Chippenham -> 12:25 Melksham -> 12:44 Trowbridge
12:58 Trowbridge -> 13:22 Westbury -> 13:33 Warminster
14:10 Warminster -> 14:57 Salisbury
(a bit of a cheat this one - through passengers would probably use the route via Devizes)