Using fridge for slow rise dough with eggs
From a food safety perspective, 48h in the fridge will be perfectly safe. (You may want to check out our generic post on storage times.)

Whether it’ll work with regards to intensifying or improving the flavor, I can’t say. Remember that the “more flavor” in regular slow-raise bread is based on enzymatic activity in the flour - which you don’t use. It may or may not be happening in the oat fiber and flax seeds. An experiment should answer that.