I don't know if the number of days using for six cases above is how many? 3 days or 10 days or...? And moreover, 上旬、中旬、下旬 and 始め、半ば、終わり which is using for month, which is for week and which is for year? Thank you.
旬 is a way to group the day of month by its second decimal digit. The days of months whose second digit is 0, 1, and 2 respectively belong to 上旬, 中旬, and 下旬. Strictly following this rule, the days 30 and 31 should not belong to any of them, but by adjustment, they belong to 下旬.
始め (beginning), 半ば (midst), and 終わり (end) have nothing particularly to do with days. It is a subjective matter what range they express.