@Graham *****
DTV visas are valid for 5 years .
You get a 180 day stamp on entry .
You can re enter for another 180 days .
You can renew once (1 time).
Which totals = 360 days .
You still need to do the DTAC .
Edit - you can extend your 180 DTV in Thailand .
You need to pay for the extension fee.
You get another 180 days .