Minor skin abrasion on top surface of foot not healing. its been 3 days and would is not forming a scab. how many days to expect healing and how to quicken healing time?

An abrasion would be a superficial wound/scrape that breaks the epidermis layer. Some conditions can delay wound healing such as diabetes, vascular disease, older age, smoking, etc. There are 4 stages: hemostasis, inflammation, proliferation, and remodeling. The link shows a good illustration of the duration of each stage: https://ykhoa.org/d/image.htm?imageKey=SURG/72355

If you are not diabetic, and have adequate pedal pulses, apply triple antibiotic cream to the wound and give it another 4-5 days. If the wound is still raw at the end of that period, it would be prudent to see a doctor. Avoid trauma to the wound site.