Never. The word from the technicians a few years ago was to either lube daily or never-both give similar tip life but occassional greasing gives shorter life( Go figure) i haven't lubed tip sprockets in well over a decade. (And I haven't burned up any tips.)
Maybe I'm doing something wrong. I now use German-made Stihl bars exclusively (I understand that in Canada, Stihl does or has used badged Oregon bars, poor northern souls). Not too much in the way of their laminated bars, which have just 10-tooth sprockets if I recall correctly. Mainly the solid bars with replaceable tips. Currently two with the "smaller"-radius 11-tooth noses, and three with the "larger"-radius 13-tooth noses (all 3/8 pitch). None of them have lube holes, nor do they need them.
My earlier experiences with Oregon and/or Homelite bars on older Homies mostly (or all?) had the lube hole.
I've never, ever greased a tip. I've never, ever lost a nose sprocket, either (knock wood). And I get considerably more than two chains per bar, hahaha!