Donna, shedding will be more frequent in the first 6-8 months of life simply because the lizard is growing at a phenomenal rate, frequency will slow down after this as the lizard approaches maturity and growth slows.
In general terms, there is no timetable for it, too many variables, such as, its diet, how much/often its fed, illness/injury burn etc, any given lizard will shed according to its needs.

re the OP the importance of regular Photoperiod (day/night cycle) is in my opinion way underestimated. Lizards and other reptiles alike, depend on these signals for seasonal cycles which trigger brumation, breeding and so on.
Nature is very gradual and consistant in this regard. In captivity your lizard relies on regular day/night cycle as much as in the wild.
My thoughts are that perhaps its getting dark outside around 7 pm and your lizard knows this (it also notices fine changes in temp as evening approaches), or conversly that perhaps it became used to a cycle where lights went off at 7 with its previous owner???
Using a timer on your lighting is a great way to ensure a consistant cycle for your animal/s.
A week or two of regular lights on/off timing will see your lizard adapt, providing it matches as closely as possible the natural day outside (remember the temp drops will give it away

)
cheers