Lighting and temp for seedling

My seeds have cracked open and will be putting them in pots and in a dome with a heat mat. How much hours of light do they need at first. I have 2 t5 to start them off. I am planning to move them outside once the weather gets better. And also what is the ideal temp and humidity for them?

I do mine 18/6 lighting look up vpd charts but around 70% rh and 75°f for seeds dont over water tho

I have them under 24hr light but tbh it doesn't matter at this stage you could have them under 1 hr a day and they'd still grow.18/ 6 is the standard cycle

Thanks. Can they stay under the t5's until its ok to bring them outside. I've read you need to transition them slowly when bringing them outside. Any advice ?

Research hardening off indoor for outdoor.
Peace.
FF