Possible Clues:

• Wee-hours work period
• Being unusually far-sighted, vary night-work?
• Serious measure — key workers are in the dark on this
• Serious measure to change unpopular work period
• Fight adversary misguidedly creating work throughout the night
• Nasty fight with adversary when there are fewer people around?
• Into work I dash, very frenetically toiling through the night?
• Late night for a working stiff ... or a hint to the circled squares
• Night duty is had very rarely in work
• Serious distance to travel for work so late