G recommends (and builds default) a 30-day Abandon Audience... your funnel might fit this just fine, or might not.
Split Cart Abandons into time periods, decreasing the bid as the length grows in proportion to your typical funnel. If your average funnel is 1.3 days (short!), do 1-2 day, 3-5 day, 6-10 day, 11-30 day, bidding the 1-2 day highest. If your average funnel is 8.3 days (long), do 1-7 days, 8-15 days, 16-30 days, and maybe even a 31-45 days. I'm just winging these numbers, there's no firm rules here, it also depends on your total volume, and the PPC man hours you have available. Point being, G gets you started with some basic plans, if any of them work for you, segment them further, bid up the pieces that rock.