My condolences on your, & your dad's, loss.
I haven't lost a spouse although I'm actually older than your dad. I think the best you can do is to ask your dad what he wants / needs & allow him whatever time he needs to grieve in whatever way he chooses. Here's a link to an article, from PC's archives. It discusses how to console a grieving friend. However I think the suggestions it offers are relevant to grieving family members as well:
8 Tips To Help Console A Grieving Friend
My best wishes to you...