last alf/grass cutting does it need to frost? newbie, please advise

Due to lack of experience I need old school advice. We took our 3rd cut of hay in southern Michigan Aug5 and it frosts usually last wk of Sept. Do I need frost to make my last cut to put the hay into dormant stage or does it not matter? Reason asking my uncle says it needs frost but everyone in the country side is going at it now. Thanks for help, I know it seems like an amateur question because I am, haha

last alf/grass cutting does it need to frost? newbie, please advise