How is "1m" more obvious that "plusMonths(1)"? I mean really, the latter is basically and English phrase. I know it's cool to shit all over OOP and Java these days, but if Haskell/Clojure/Whatever had a function (plusMonths dt 1) or something that, you wouldn't call it a pile of FP.
I said elsewhere id add a letter to distinguish months, minutes, etc. Otherwise, you missing larger picture: it's a time series analysis language with an expression adding a value to a date. So the value's letters are a datatype or unit of time. That simple.