Do you have set times of the day that your LO gets screen time? Do they have to 'earn' it in any way?

I've been really chill about the screen time lately with it being cold out, and when I am solo parenting all day I cave and let them play the phone or watch TV. My youngest stopped napping, so when I want her to rest I let her have my phone, which is probably terrible. I really need to cut back on this, but my sanity says otherwise.