Notice the crack running down along the horn in the first pic. This will be filled with thin CA glue, then over again with thick CA glue, finally hide glue will go down in it before the sinew is glued down. If i haven't mentioned it before, the inside of the horn will be the bows BACK, to be covered in sinew. The outside of the horn serves as the belly of the bow.
After both horns are lashed they are set behind the stove inside the house. It gets warm there, but not hot. In the summer they could be left in the shop, but with temperatures here being below freezing, they wouldn't cure and would just freeze. Tom estimates about a month for them to dry, emphasizing the importance of making sure they are fully dry before removing the lashing so they don't try and bend back.