The 45 day thing is solid but i'd push it even further depending on niche. christmas stuff i start refreshing creatives like late september cause pinterest needs time to test and distribute before the actual searches peak. by the time people are actively searching your pin already has some traction.
one thing nobody mentioned... the search volume on pinterest for seasonal terms ramps up way earlier than people think. trends tool shows the spikes usually start 1-2 months before the real season. so if you wait til the season is here you already missed the climb.
seasonal isnt dead at all imo, its just not passive anymore. you cant set and forget like the old days. fresh pins, same urls, plan ahead and it still works fine. the people saying it dropped off are usually the ones reusing the exact same image every year and wondering why it died.