In fact it says "It is SO hot" and "normal English" for that is "very hot". "Non ho tanto tempo" = I don't have as much time (as I would need to do things properly) >> I don't have much time. Some other example: (ho due euro) > non ho molto denaro. More or less absolute, two euro is just not much. 'Ho tanto denaro" I have (so) much money.
In many languages speaking about the weather is done idiomatically. Italian uses the verb "fare" (which, by the way is also done in French, who use "faire") to speak of the weather. "Fa freddo oggi" = "It's cold today", and the adjective is always in the masculine singular form. "Fa freddo/caldo/fresco/brutto...." BUT a different idiom when you want to say things like, "It's sunny today" = "C'e' il sole oggi." "C'e' il vento" = "It's windy." Hope this helps.