Check out this mention of General Finishes's Enduro Extender in Family Handyman Magazine, July/August 2013. Thanks for the shout-out, familyhandyman.com.
Use an Extender in Hot, Dry Climates:Water-based finishes are more sensitive to temperature and humidity than their oil cousins. It's best to apply your water-based poly when the air temperature is between 70 and 80 degrees F and the humidity is below 70 percent. If the air is both hot and dry, the poly may set so fast that it will
be difficult to maintain a wet edge as you brush, or the film may not level properly before it sets. The solution is to add an extender to slow the drying time. This is especially useful when you're coating a large piece like a dining table. One choice is General Finishes Dry-Time Extender, No. 21217, $12 per pint at rockler.com. Floetrol is another great additive for slowing things down. It's designed for latex paints but works great with satin or semigloss water-based poly and is readily available at paint stores.
Available at Rockler & Woodcraft Woodworking stores, or use the store locator to buy in the U.S., U.K. and Canada.