Immigration question

Hi everyone :), I was recently in Zambia and it was my first time visiting my partner and I enjoyed it so much (very beautiful country and lovely people). I used the bus from Zim to Lsk and they gave me 90 days (9june-Sept)by Chirundu border post. I used up 27 days and I am back home in Zim now. I would however like to visit my partner again for maybe 4/5 days this July. Then come back in December for a bit to spend the holidays.

My question is this- are the 90 days for one actual year i.e 2026 or does the year start counting from the day you enter the country ie June 2026-June 2027. Because in that case when I completely use up the days remaining, in December 2026/Jan 2027 then I will not be able to return until June of 2027 again. Also would they give me another 90 days every year?

Do you advise flying in or using the road in relation to this particular scenario? Or it would not make a difference? Ps I am Zimbabwean if that matters. Any help/answers are greatly appreciated❤️.