Peak dates, and the single thing they change
A peak date is one of the handful of dates the house names when asked, and the only thing it changes is that half the fee goes ahead beforehand.
A handful of days and weeks each year fill this city completely, and those are the peak dates. The house does not publish the list and it does name every one of them to you the moment you ask, because a guest arranging an evening deserves to know whether the date is one of them before anything is agreed.
What they change
One thing only: a booking on a peak date carries half the fee ahead, whatever else is true about it. A returning guest who would otherwise settle a same-day hour entirely at the door sends half ahead on a peak date, and that is the whole of the difference.
What they do not change
Not the figures. An hour is EUR 180 on the last Saturday in April exactly as it is on a wet Tuesday in February, and there is no seasonal loading anywhere on this site. Not the arrival window either, which stays at forty to sixty minutes across the centre even on the days the streets are at their fullest.
What they do to availability
They make it narrower, which is a scheduling fact rather than a policy. On a peak date the roster fills earlier in the day and a message sent at ten in the evening has fewer names still free than the same message sent at two in the afternoon. Nothing about that is unique to this city, and the fix is the obvious one: write earlier. The spring page covers the busiest run of them.