Working irregular hours in the games industry means you would still work daily but it would depend on what you do. For example you may be typing in code and scripting for a gun shooting. So you would come in at 8am then leave when you finish and the next day you'd be writing coding on a charater firing the gun so you come in at 8am and leave when you finish and so on.
With working irregular hours you'd get paid on how long you worked there so say you earn £10 an hour and you finish what your meant to do in 3 hours you'd be paid £30