HOW LONG SHOULD I WAIT IN BETWEEN HIGHLIGHTS?  Usually at least 8 weeks, since you need enough regrowth (1 to 2 inches) to touch up....If you can't stand any amount of rootage, cover it with a temporary highlighter pen until your next dye job.  A few face framing highlights will do the trick.  Try Oscar Blandi Pronto Colore Root TouchUp and Highlighting Pen.