So when Malory started walking Dori had 1000 steps...So it would take Malory about at least 11 minutes...but in 11 minutes that she walks,Dori would have 1550 minutes walking so if they keep going and stop at 1:00 both of them would have at least 3000 minutes walking cause 50 x 60 = 3000 and 90 x 33 = 2970 and if you round you'll have 3000.
So I would either think 11 or 33 minutes Malory will need to catch up.