I may be two-tenths of a split-second late

A playfully-overprecise remark that you tell someone to let him know that you may be briefly delayed in meeting up with him, and so he should simply wait for you if you don't arrive at precisely the moment when you said you would.

Cool dude, texting to his buddy on his smart-phone as he's hurriedly scuttling along the downtown sidewalk: "I've had a last-minute errand that I gotta run real quick, so I may be two-tenths of a split-second late --- no worries, though, Bro --- I'll still shoot some hoops wif youse, just as I promised."