My honest answer is whenever you can or have time. In a perfect situation, I would love to be able to meditate in the middle of my day to recente myself and right before bed to reduce screen time and achieve a truly calm state so that I can ready myself to go to sleep. However, my toddler tends to not permit this every day. So figure out when is best for you and that will be the best time to meditate.
For me, I meditate before sleeping immediately. It helps relax and fall to sleep faster. But I imagine meditating in the afternoon would be helpful too, especially in stressful days.