Implantation bleeding is actually very rare. Many women mistake breakthrough bleeding or light spotting or their period for implant bleeding. You may just be starting your period early. Every woman has off cycles at some point for a multitude of reasons. With that said, it never hurts to test. But I would wait to see if the flow gets heavy like a period. If not, test on the day that you would've missed af or after the bleeding stops, whichever happens first
If your bleeding I wouldnt test at all yet, see what happens with the bleeding first, if it ends up by getting heavy and like your regular period, it may have come early, if its lighter or shorter than what you normally experience then test after you have finished bleeding