When to stop veg nutes and start bloom nutes?

I would follow your feeding schedule from the brand of nutrients your using. They list if your Veg/Flower is going longer and what weeks to repeat to off set this according to their schedule. https://lotusnutrients.com/pages/easy-guide-and-recommended-hydroponic-feeding-schedule there PPM scale is a bit high though, use the ratios they are suggesting between grow : bloom, but dilute your overall solution. Also have to remember autos feed lighter then photoperiods. https://www.autoflower.net/forums/threads/med-man-method-feeding-chart-ppm-ec.47856/ This link is a good reference for how much to feed your autos in terms of PPM/EC, its not 100% so you need to look at your plants and if they need less or more adjust with accordance. The plant will show sex first with pistils, then stretch and go into flower. I would keep your grow nutrients till its mid way stretch then start mixing in in the bloom. Best Of Luck!