Can someone please explain to me the rule(s) behind czas turning to czasu. If there are any other online sources that you know of too that could help understand Polish grammar that would be great to know!
Mam requires accusative
If a verb is negated accusative changes to genitive
genitive form of czas is czasu
you can look for some often recommended resources here https://www.duolingo.com/topic/922/top
this book http://www.skwierzyna.net/polishgrammar.pdf is good.
Pls, answer me!
Cannot I use "Godzina" in this case?
No, "godzina" doesn't mean "time", it means "an hour".
I presume that what got you confused is "What time it is?" which translates to "Która (jest) godzina?", but those are idiomatic phrases which are not equivalent in terms of vocabulary.
Thank you for your comment, it helped me a lot
Is the object of a negative verb ALWAYS in the genitive, irrespective of what case the positive verb takes?
No, only if the positive verb requires accusative or genitive and the case is not governed by a preposition.
So, just to make sure I've got this right - the negative of (say) POMAGAM DZIECKU is NIE POMAGAM DZIECKU - not NIE POMAGAM DZIECKA?
That is correct. The negation only matters if the positive sentence used Accusative.
No, it's true, I really don't have time.