There is an older thread with some research papers linked in the replies, but I don’t think any were specific to hazels (and I assume different species have different pollen viability in storage):
(actually, looks like both links are broken now, oh well)
I will be doing avocado hand pollination in my greenhouse again this year (the earliest varieties will be opening soon), but still haven’t found a method of collection and storage that I like. I’m thinking I need to spend an afternoon wandering the Container Store in search of inspiration.
My biggest problem is the anthers and nectaries are too close in avocado flowers, so I end up with clumpy pollen glued together with nectar, and nectar on my brush, meaning the pollen is hard to dry out for refrigeration or freezing. I assume that’s not an issue with hazels.