What is the min time for understand javascript

That depends on you. The sooner you start, the sooner you'll achieve your goal. Here's the course: https://www.sololearn.com/Course/JavaScript/?ref=app

It depends on. Typically to learn something new it takes roughly 20 hours according a study. That's 1 week: 3 hours a day. or little over 3 months : 15 min a day. Good luck.