Long retargeting windows used to be a safe default. With shorter attribution lookbacks and tighter privacy constraints, a 30-day window often just burns budget on cold-by-then traffic.
What the data shows
Across the accounts I manage, the marginal conversion rate of retargeting impressions drops sharply after day 10-14 for most consumer categories.
A better default
Start with a 7-day window and a separate 14-30 day window at a fraction of the bid, rather than one blended audience treated the same way regardless of recency.