I've found the cold hide glue (sold in the USA under the Titebond name)
useful when slow drying time is needed. It is kept in a liquid state,
I believe, by the addition of urea. (This may be purchased at a
hardware or garden store, as it's also used as a fertilizer.)
As previously mentioned here, you may also add urea to slow drying time
of hot glue. I was warned by several piano technicians, however, that
the cold glue does not have the strength of hot glue.
One tech said he regularly used it in gluing bass bridges until he was
told not to. Experimenting, he struck a cold-hide-glued bridge a smart
blow with a hammer and it fell off.
Since then, I've used only hot glue where strength is critical. I use
fish glue similarly. It gets a tack very rapidly and I like it for
gluing on felts and leather punchings, etc. It also smells good (not
West Chester, PA