For most smooth and standard dancers of average to above average skill level, the most pivots that can be reasonably squeezed into a single measure of Waltz is 4. Two pivots (presumably canter timing) are going to die a slow death at Waltz tempo, and so we are left simply with two choices: 3 or 4 pivots per measure.
3 pivots in a measure would in all but very rare circumstances be counted straight: 1,2,3.
As for 4, here's where you have options. The most popular timing is "1 and 2, 3", since it results in a very Waltzy lilt at the appropriate time, counts 2-3. However, there are times you may wish to modify that timing slightly, based on a number of factors such as what you're dancing before or after the pivots. With a single syncopation, we can presume that 3 of the steps will be taken directly on the beats, which leaves us with the choice of which "and" count to attach that extra step. In total, you have 3 "ands" in each measure, so take your pick and see what kind of timing it leaves you with, e.g.:
"1 and 2, 3"
"1, 2 and 3"
"1, 2, 3 and"
Technically, there's a fourth option if you use the "and" count from the previous measure, e.g. "and 1, 2, 3".
Someone will probably come along and say it's possible to double-syncopate a measure of pivots, i.e. take a total of 5 steps, two of which would fall on "and" counts. Of course, just because something is possible doesn't mean I'd necessarily recommend it. Nonetheless, if you really want to give it a try: (1) Good luck, (2) Use the same method above and simply choose two "ands" to attach the two extra steps, (2) It's probably better to put as much space between those "ands" as possible, such as "and 1, 2, 3, and".
Regards,
Jonathan