I use Titbond for 90% of my model building (most of my models are 1/4 scale) and I have found it is best not to handle for at least 4 hours, wait longer if the weather is cold. It really takes at least 24 hours before full strength is achieved but you can usually handle safely after about 4 hours. Hotter and drier speeds up the process, high humidity seriously slows the time for achieving of full strength. Another often unknown characteristic of any aliphatic (like Titebond) is it's thermal characteristics. If you spread a thin coat on an object, let it dry, then mate against another materieal, heat and prestoinstant bond.