Your girls look soooo happy out by the pool!
Probably at least 3 days- but...in the pic, we're looking at at least two generations, so a week may be a closer guess as to when they first got there...It's a real good thing you spotted them when you did, because every
adult aphid can have about 12 babies a day...so that would be 100 aphids one day, 1300 aphids the next day, all females, all born pregnant, ready to have babies in 3 days...they're like covid with legs...
Outside at night is when the moths lay their eggs, so in 4 or 5 days you've got caterpillars crawling around on your plant...so, the less time they're out there at night, the better....
Moths are the only reason I bring my outside plants (the ones in pots) in at night...
Your plant can get caterpillars from butterflies too, but that doesn't seem to happen very often-
Butterfly caterpillars are usually pretty big, so they're easier to spot - I found a 3 inch long green one on my CBD plant a couple of years ago...