"Do you have time today?"
Translation:Macie dziś czas?
It's usually the last word in a sentence. Sometimes it's also 'the one put in an unusual, but still correct, place' - but then of course one needs to know what 'usual' is ;)
So in "Masz dzisiaj czas?" the most important word is 'time', which seems logical - I'd say it's a neutral question.
In "Masz czas dzisiaj?" it's like "Do you have time TODAY?", as in "OK, so we need to deal with this matter some time this week... actually, are you free today?".
The verb mieć takes the accusative case in positive sentences, so only masz czas is correct.
Czasu is the genitive case form, which is used in various other situations, for example:
- Nie mam czasu (genitive for direct objects in a negative sentence)
- Mam trochę czasu (genitive after quantifiers)
- Od czasu do czasu (genitive after prepositions like od, do or bez)
- Chwila czasu (genitive to indicate possession or reference, similar to English "of")