I recommend man timezone
Basically the 0 in PWT0PST means that your offset to GMT is 0 hours; but there is a daylight saving time in effect, which is somehow called PST (could this be 'Portugal Summer Time' ?? (and PWT the same with Winter?)
There is no case of worry if you always use the same method of getting your time.
The timestampe method has the additional advantage that you won't get double values even during that one hour in autumn when you switch back to winter time.
By the way, 'date -u' always gives GMT, in summer and in winter.
hope this helps