let me know how long do you think I have to harvest

To get the best idea of overall ripeness you need to look at the whole bud. Some parts of the flower are older than others and trichomes can be ready on some small older bits of the flower and if you look at those up close it will look like you need to chop, but the rest of the bud might be a few weeks younger and not ready yet. The trick is to harvest when the bulk of the flower is ready and that you can only tell by looking at the entire plant. Checking trichomes causes more confusion than it's worth IMO