1) Probably a day's labour, done by the day and paid by the daily rate.
Colliers working in a Bradford pit claimed that through the dangerous activities of a competitor they had, on 3 July 1702, been forced to give over … before their day works were ended. This may simply mean that they had to stop working on that particular day, but ‘day-work’ could also be day labour, that is work done by the day and paid by the daily rate. In Colsterdale, ‘when the men worked for day wages, the owners paid for candles’.
2) The amount of land that could be worked in a day.
The Halifax historian John Watson wrote in 1775: The measure of land used in this parish is at present by day-works instead of acres, though the custom seems not to be very antient, for the word acre is always to be met with in writings of any long standing. He calculated the day-work at 3,136 square yards. It is actually a usage recorded as early as the thirteenth century in East Anglia but has not yet been noted in Yorkshire until later: 1545 two dayes worke with a plough in the Nethercroftfeld, Huddersfield
1595 one daye worcke of land in the field called Sowthcrofte, Norland. The Yorkshire cartographer Christopher Saxton used daworks on some maps as a land measure and the term remained in use across the county: 1642 The South Wandell close with its bottomes is 8 dayworkes, or will serve one Mower eight dayes, Elmswell. It became a frequent field name.