וַיִּרְבּוּ֙ הַיָּמִ֔ים וַתָּ֖מָת בַּת־שׁ֣וּעַ אֵֽשֶׁת־יְהוּדָ֑ה וַיִּנָּ֣חֶם יְהוּדָ֗ה וַיַּ֜עַל עַל־גֹּֽזֲזֵ֤י צֹאנוֹ֙ ה֗וּא וְחִירָ֛ה רֵעֵ֥הוּ הָעֲדֻלָּמִ֖י תִּמְנָֽתָה׃
過了許久，書亞的女兒，猶大的妻子死了。猶大得了安慰以後，就和他的朋友亞杜蘭人希拉上亭拿去，到他剪羊毛的人那裡。
Rashi
ויעל על גזזי צאנו AND HE WENT UP UNTO HIS SHEEP-SHEARERS — it means: and he went up to Timnah to stand by his sheep-shearers.
Ramban
AND JUDAH, WENT UP UNTO HIS SHEEP-SHEARERS. He would go there continually to console himself after his wife’s death so that he may turn his attention to the sheep and forget his poverty.170Proverbs 31:7. [and remember his trouble no more.] Now when it was told to Tamar that he goes up there daily without fail, she waited for him on one of those days. It may be that since Judah was prominent in the land, people would assemble there to make a feast at the time of the shearing, similar to a royal feast, and the poor would go there, and it was told to her before he went up there.
Radak
וירבו, according to Bereshit Rabbah 85,6 the time frame discussed was 12 months.