My method is take an educated guess multiply by 2 add 1 as extra buffer and then change it to the next unit, e.g. day->week, week->month, months->quarter. So for something that it should take 1 day I'd say 3 weeks. It seems a lot but at the end there's usually so much red tape, burocracy and and technical debt that it usually ends in the latter ballpark.

Nice algorithm!