I top and top and top and top -- you can top as much as you want. Sort of like mud said, you have to make sure that your light has a big enough footprint to cover all your tops. I would keep topping it if you only have that one plant under a 240 watt led. Topping does, especially on soil, slow vegging growth somewhat but it will pay dividends in flower after your stretch. That's just my opinion and everyone has their own style so just play around until you find what works best for you. Here's a link to my garden -- I veg under 240 watts of cheap walmart fleurescents -- topping constantly :
https://www.rollitup.org/t/grow-chop-dry-cure-repeat.852792/