How many days does the 30-month presence requirement for the US?
It doesn't work that way; the above describes how Canada's physical presence requirement works which is 1095 days in a four year period. The US standard is continuous residence. Any absence from the US of more than six months breaks the accumulation of the most common period of five years residence in order to apply for naturalization. One must then start over from zero. There are exceptions, of course, but for your average LPR, this is the rule.