I can find lots of references to the pay rate of the Tolpuddle Martyrs (originally 10 shillings a week, then reduced to seven shillings and were due to be further reduced to six) but how many hours a week were they expected to work for it?
I did not find a specific reference to the work hours of the Tolpuddle Martyrs either. It's possible they worked radically unconventional hours, but probably it was no different than the norm at the time. That is to say, 12 hours a day (less meal time), in the summer. This would've been reduced in the winter in accordance with the much shorter days, so about 8 to 10 hours a day.
The traditional summer hours for many ordinary labourers in southern English counties had been from 6 a.m. to 6 p.m., with breaks for meals (customarily half an hour for 'breakfast' at mid-morning and an hour for the midday meal). These hours were still found in the 1860s in Northamptonshire, being normal on the estate of Lord Exeter; winter hours were during daylight only.
Thirsk, Joan, ed. The Agrarian history of England and Wales. Cambridge University Press, 1985.
Dorset being one of the counties on England's southern coast, presumably the Tolpuddle Martyrs worked something similar.
This is also why around the same time as the Tolpuddle Martyrs, there was a general labour movement demanding an 8 hour work day for 12 hours of pay. Less ambitious unions commonly included 10 or 10.5 hours working day as a major plank of their demands.
The 'Society for National Regeneration', based in Manchester and headed by Robert Owen and John Fielden, aimed at 'an eight-hour day for twelve hours pay', but folded with the collapse of the Owenite general unions in 1834.
Wright, David Gordon. Popular Radicalism: The Working Class Experience 1780-1880. Routledge, 2014