וַיָּבֹא עֲמָלֵק וַיִּלָּחֶם עִם־יִשְׂרָאֵל בִּרְפִידִם׃
Amalek came and fought with Israel at Rephidim. (Ex 17:8)
When exactly was it, what day was chosen to fight the Israelites and why that day - what special weaknesses are known for it?
I'm trying to understand Haman's tradition in "Was purim-in-adar-hamans-choice-or-a-toss".