Hi xspeciem
There are few case reports available via pubmed/epub in which Lamotrigine itself induced persistent visual snow and palinopsia/trails in patients with migraine, who got no such symptoms before.
But also there are few reports on patients with PHHD and migraine who had their visual perception improved on Lamotrigine, so possibly it is not solution for everyone and potentially can make PHHD worse.
I found no data on this. The mainstream hypothesis now is that aeropsias/palinopsia/etc are generally related to a hyperactive visual cortex, which is possibly determined by the genetics and/or early stages of development.
If this hypothesis is correct, then PHHD (and permanent aura in migraine and epilepsy) are possibly pre-existing conditions, you only notice them when cortical self-inhibitory mechanisms become downregulated or somehow insufficient to inhibit excessive activity in visual analyser which allows it to generate all that weird stuff out from nowhere. So possible time from onset should not matter at all, this thing is there much longer then you notice it.
Although there are some personal opinions that PHHD related symptoms tend to improve over time span of years-decade on it's own.