A three hour boil is good but you have to keep adding water, you need to chop up your sinew into small pieces, when you boil it keep it on a low boil, mash all the excess liquid through the sinew pieces through a grease screen when finished. I have made and used boild hide glue for over 20 years and it works great, it will be less tacky than commerical grade liquid or even granual hide glue, it will make like a jello consistancy and if not put in the freezer it will mold over time, if you spread it thin enough in the pan it will harden. You just put in a double boiler on low heat with water to re-constitute. Homemade glue is much better than commerical grade. It will seem very watery when you use it but will dry hard and faster than commerical grades, The tight bond liquid hide glue has a retardant in it that keeps it from drying to fast. You can take the glue you made and after only 5-7 days with one layer of sinew backing brace your bow as long as it was left to dry in a warm area of the house. Oh you can also add pieces of rawhide to your mixture if you have it, doesnt matter if its elk, deer, beef, moose..etc.. but it's not nesscary.
This statement is from experience and over 200 sinew backed bows not taken from internet forums or books, just trial and error over almost 3 decades of making sinew backed bows!
good luck!
Eric