Question
How do i know when its time to pick my cantalopes so they will be ripe, also watermelons?

Answer
If they are true cantaloupes, they will tell you when they are ready by coming off the vine easily.
Other melons aren't so easy to tell.  As the rind loses its green color, begin checking daily by giving the fruit a very slight tug, when it's ripe it comes right off. If you like them on the firm side, don't wait until that point, just pull it off when it has lost all it's green color.

It is especially difficult to determine ripeness in watermelons. I have had the best luck using a combination of two indicators. First, the tendril nearest the melon will be completely brown. Second, the 揼round spot?will be yellow. This is the place where the melon is in complete contact with the ground. If you check it and it is not yellow, be sure you replace the melon in the same position, or you may not get a good reading next time.