Can't manage to sort a file and display time & date on a LCD screen.

Projects Programming
13

so what do I write in SD.begin()?

4, just like you had.

Would it be possible?

Of course it would.

The programme only takes 16 454 bytes whereas the uno can store twice more.

That's flash memory. You are likely running out of SRAM.

You could recover some by using the F() macro:
Serial.println(F("initialization failed!"));