Quetiapine for anxiety

[Ikeatears]

I'm currently taking 50mg morning and night for anxiety and insomnia. It helps me sleep and the morning dose, I take very early (6-7am) so that the sedation wears off more quickly and I can function during the day.
I am also taking 45mg of Mirtazapine at night but this is a relatively new dose and I'm waiting for it to 'kick in'. By about 5pm every day, I feel my anxiety returning and I have to manage until bedtime when I can take my meds.
My problem is this. I will run out of quetiapine tonight and will have to try and get an emergency script tomorrow (obviously I'll have to take it later than usual) All fine except when I rang home treatment for advice, she said because I've been taking it so long (about 5 weeks) a missed/late dose shouldn't make much difference as it's been in my system for this length of time. That doesn't seem to be my experience though. I feel like I can feel it 'wearing off' around 8-10 hours after I take it. Is this in my mind or is it the experience of other? It's immediate release if that makes a difference.