Do not know if it helps or not, since I am not acquainted with Punjabi, but in Persian, which is intensely related to Punjabi, "eftaarii" stands for, let's say, the "meal" which is either eaten or served for "eftaar" (< "act of breaking one's fast after hearing Maghriib Adhaan"). However "eftar" too can be used in that sense, but "eftaarii" cannot replace "eftaar".
Here are some sentences to exemplify it: "eftaar chii khordiin?" / "eftaarii chii khordiin?" ~ "what did you eat for iftar?"; cf. "eftaar kardiin?" ~ "did you break your fast [after Maghriib Adhaan]?" but in this last phrase I believe it is improper to use "eftaarii" instead of "eftaar".
I can but confirm the explanation by Phosphorus SaaHib and the cited meaning from an Urdu dictionary.
میں کل افطار لئی اوہناں دے گھر مدعو ساں تے افطاری وچ گاجراں دا حلوا وی آیا سی۔ maiN kal iftaar (aftaar) la'ii óhnaaN de k_har mad3uu saaN te iftaarii (aftaarii) vich gaajraaN daa Halvaa vii aayaa sii.
PG SaaHib, technically speaking, the correct word is "iftaar" (for LP's benefit the "t" here is different from the "t as in "tel". With this "t", we find words such as "taaqat", tuufaan, talaaq, tanz etc). The "y" in the word is a mere "padding", just like "xush-xabarii" where "xush-xabar" would be the correct form.