Lex after spending almost an hour to activate the Land Elemental Energy Form, had gathered that he was able to sustain it for 5 minutes without much strain and 10 minutes without any fatal or serious backlash.
However, this was with Lex not using the Land Elemental Energy Form much as he wasn't in the heat of battle where he would have to use much more energy, so he estimated that 5 minutes would be his limit if using it in battle.
Lex spent 8 minutes in the Land Elemental Energy Form and found that his movement speed underground was extremely quick to the point where he shocked himself and it wasn't much slower than his full speed on foot.
But he also found that travelling underground was very tiring and straining on his Land Elemental Energy Form that couldn't sustain itself for too long.
The final thing he tested was Geokinesis, the ability to manipulate land at will, and found that the land followed his will.
