Messiah was to come after the 69th sabbath cycle.
The unit of time-measurement appears to be cycles of sabbatical years, here translated ‘sevens,’ traditionally ‘weeks.’
The starting point seems to be the command of King Artaxerxes 1 in his 20th year (445 BC).
The sabbatical cycle in which this starting point falls is 449-442 BC.
Using the usual inclusive method of counting, the 69th cycle is 28-35 AD.