Normally, in full time occupation, if you work the whole of January, February and March you are entitled to half one month's pay at Pascha. If you work the whole of April, May and June then you are entitled to half one month's pay at the summer holiday. If you work the whole of July to December you are entitled to one full month's pay at Christmas. For any of these periods where you don't work the full period then you are entitled to a fraction of the payment in proportion to the time worked.
I am not certain what they do when people are doing seasonal work. Logically, anybody working from the beginning of May to the end of October, i.e. six full months, should be entitled to one full month's pay. When exactly you would be paid it I don't know.