blink without delay

OK, I understand the delay process and have used it on a few sketches now, but I would like to dive into the "miils" part of sketches. I would like to know how to contol both high and low rates of blink without delay. I am making LED strobes with 10watt LEDs for Halloween projects which I am uploading onto an ATtiny85. I would also like to run 2 indenpendent strobes using a single ATtiny85. I know, Halloween is a long way out but I start designing the yard in June, and my PLC program is complete by Sept. with minor timing tweaks after the props are setup. Dave