What is the correct height for light from soil using 240w LED and two plants in 1x1m tent?

You should measure from the light to the top of the plants, not to the soil level, it is the leaves that count, not the soil. Generally in veg/seedlings and depending on your LED, around 2 feet/60cms between the top of the plant to the underside of the light is about the average distance. With your 240 watt I would be running it at 100%. and with both the "veg" and "bloom" lights switched on if your light is so equipped. Whenever I have used an LED (450 watt) light, I have both the "veg" and "bloom" switched on and at 100% right from day one, this seems to produce the healthiest growth and seems better than using just the "veg" light switched on, on its own. Hope this helps, .......... Organoman.

I would say around 70-90cm but it really depends on the brand of light, every light will come with recommended hanging distance guide for an stages of growth, it's just about finding that sweet spot🌱👍

27c is OK but I wouldn't let it get too much warmer. Judging by my lights, you can't just say 70%. The light power adjustment can be fussy. Sometimes a small adjustment can have a big affect on output. Better would be to use a light meter or an app on your cell phone or maybe see how much power your light is consuming with a Kill-A-Watt to determine how much light horsepower you are putting out.