I have little experience with traditional hammer veneering, so defer on the technical aspects, but suggest that the warmer the work and the lower the gram strength, the greater the working time. In my limited experience with the technique, the thicker the glue, the more tenacious the tack, but the shorter the working time. I prefer hide which shows about the same consistency as honey at about the same temperature, and is described by many as - no surprise - the consistency of hot honey.
Also note that fresh hide is easily melted with heat alone, so hide may be brushed onto two surfaces to be joined, allowed to cool, joined, then heated to bond. This does not work for edge joining, but for veneer work and thin plates does pretty well.
Another consideration is to warm the glue-soaked surface with a good heat gun or heat lamp...we have several in the shop for warming bridges for saddle removal, but they work as well on small surfaces. On the one Jefferson desk I did with sawn veneer, this was the approach taken and it worked well enough.