The Captain's ten or twelve hours of daily work was performed, no doubt, at irregular intervals,--some days late and some days early,--for he might be seen about Norwich almost at all times, during the early part of that November;--and he might be very often seen going into the Close. 
The Captain's ten or twelve hours of daily work must have been performed at irregular times, for he might be seen about Norwich at all times of day, very often going to the Close. 