In determing the time when using the Black-Scholes formula, and suppose the time is 30 days, do I convert to years and use 30/365? Or do I use 1/12 and think of the 30 days as one month? Or does it...

In determing the time when using the Black-Scholes formula, and suppose the time is 30 days, do I convert to years and use 30/365?  Or do I use 1/12 and think of the 30 days as one month?  Or does it even matter?

I was also wondering if I would ever just use 252 since that is the number of trading days in the year?  So, for example, 30 days would be 30/252 of a year in the Black-Scholes formula?

I think the calculations all lead to minimal differences, but I am wondering if there is a set rule or standard protocol?  Thanks!