How to switch over from 250W MH to DIY fixture on 20" cube

[nerdz]

As title, states I have no idea how to make the switch without risking my livestock.

My current 250w MH bulb is quite old, as I knew I was going to LED. Tank is a mix of LPS and SPS RBTA

*My LED setup is as following:

8 x XM-L neutral whites driven at 2.3A
14 x XT-E Royal blues driven 1.3A
6 x UV and 2 x red driven at 700mA

It will all be controlled by a ReefAngel, so I have lots of options about dimming and lighting cycles.*
So, # hours?% to run at?

Thanks for any help!