What is the difference between "to work on overtime" and "to work overtime"?
From articles.latimes.com/1988-04-08/local/me-1185_1_gang-violence
"Police Chief Daryl F. Gates promised to conduct anti-gang sweeps with 1,000 officers working on overtime after the Good Friday gang shooting that killed one person and injured 12."
There is no difference in meaning and "working overtime" is the more common expression.