How to know last 2 weeks of grow?

Hi everyone, I'm growing sativa and don't know how u tell when it's the last 2 weeks. I wanna use a boost and don't know when to start?

Look at your tricombs using a 30x jeweler a loop. Look for clear, milky and Amber colors.. For me.. If it's the last two weeks you should see mostly milky trichs. When you harvest... Some ambers

Thank you. I'm a first time grower and want all the advice I can get.