I took premarin for a while and I normally took it in the morning, only because that was the most convenient time for me. I would be more likely to forget to take it later.
My worst meno symptom was also insomnia and I found taking it in the morning was fine.
I remember reading about dosing times for premarin versus estradiol tablets, and apparently estradiol tablets are most effective for the first 12 hours so taking it at night would be better for sleep issues. However premarin had a longer effective time (closer to 24 hours) so dosing time didn't matter as much.
However, maybe a better option for you would be to consider patches. Estradot is a good estrogen only patch. I'm not someone who demonises "synthetic" HRT, which is what premarin is, because I believe women should use what works best for them, but patches do give a much more consistent dose, and because they're absorbed through the skin and don't have to be digested, the overall dose can be much lower than tablets.