my mum died at a similar time of day just over 2 months ago. I know how hard it is but things are getting a little easier for me. I find that, as time goes on, I am remembering the times pre dementia (and my mum was ill for around 15 years) and that is making the loss a little easier to bear.
The early days were horrendous and the depth of my grief and pain took me by surprise - I thought I had lost my my mum years ago and expected her death to be a 'happy' release. However, with hindsight, I realise that we did lose her years ago in many ways, but you don't really get the opportunity to grieve for someone while they are still alive,because you are too busy dealing with the here and now.
The best advice I can give is that you need to deal with things one day at a time and not look too far ahead (or behind!)