From Longman Dictionary of Contemporary Englishbe quick/slow/first etc off the markbe quick/slow/first etc off the markinformalUNDERSTAND to be quick, slow, first etc to understand things or react to situations You’ll have to be quick off the mark if you want to find a job around here. → mark
Examples from the Corpus
be quick/slow/first etc off the mark• Salad crops, however, are quick off the mark.• This time, they were slow off the mark. 