is .... za pierwsza?
za (minutes) pierwsza
is... minutes to 2 o'clock is ... za drugesta? etc...
za (minutes) druga
is... past 3 o'clock ... po trzej?
it's trzecia, so:
(minutes) po trzeciej; za (minutes) trzecia
the thing is while 'po' refers to godzina/ the hour - (po trzeciej - after/past three ) 'za' refers to minutes and godzina is not affected (and remains in nominative)
is... past 9 o'clock ... po dziewatnej?
is... past 10 o'clock ..po dziezatnej?
po dziewiątej po dziesiątej - kwadrans po dziesiątej - quarter past ten - za kwadrans dziesiąta - quarter to ten
the endings -ta -sta -wsza -ga -cia that you can use with (respective) numbers is only to depict that a number should be read as ordinal much like the English 1st, 2nd, 3rd, 4th and so on
so you've got 1-sza or 1-wsza (in singular for a female gender which applies to hours)
11-ta or 11-sta
the thing is ordinal numbers decline like adjectives so you also have 1-ej for female gender (in a couple of cases)
I suggest you learn the pattern of declination for adjectives in female gender (for a start) - it's actually the simplest declination pattern for adjectives only two forms are present you just need to know which forms to use for which case