"The authors have used daily maximum temperature as the measure for water stability, ignoring the diurnal cycle at each location. Therefore their statement that water may be stable in some locations for 34% of the orbit (year) is incorrect. Water may be stable at some time on 34% of days, during the year, but typically for short periods of time on each such day, so the overally stability is much less than 34% of the entire year."

I would more likely say their phrasing is ambiguous rather than being incorrect here.
In a report given at the 2000 LPSC conference also cowritten by Chris McKay the authors also estimate periods where liquid water might be stable and also use phrasing that would lead you to believe they mean this stability phase is continual day and night over this period:

Meteorological Control on the Formation of Martian Paleolakes
Authors: Haberle, R. M.; McKay, C. P.; Schaeffer, J.; Joshi, M.; Cabrol, N. A.; Grin, E. A.
Journal: 31st Annual Lunar and Planetary Science Conference, March 13-17, 2000, Houston, Texas, abstract no. 1509
"Results: In Fig. 1 we show the model predictions for where, and for what length of time, liquid water could be
stable on present day Mars over the course of a year. According to the model, there are five distinct regions where
pressures and temperatures are above the triple point, but below the boiling point: near the equator in Amazonis,
Chryse, and Elysium, and in the impact basins of Argyre and Hellas. A plot of the number of degree days above
zero (not shown) gives a similar distribution with the maximum in each location well above 10 days - a typical
value for the Antarctic dry valley lakes. Thus, requirements (2) and (3) can be plausibly met though there is still
the issue of melting the ice before it evaporates [5]."
http://adsabs.harvard.edu/cgi-bin/bib_query?2000LPI....31.1509H [full text]

The Fig. 1 they mentioned here is also captioned by:

"Fig. 1. Duration (Sols) and location where liquid water could be stable on present day Mars."

It is only by email correspondence from one of the authors that you gather that they mean that over this period, say 10 days, the water may be liquid for short times during the daytime for each of these days.

Bob Clark