I think a very short lived cert (like 7 days) could be a problem on renewal errors/failures that don't self correct but need manual intervention.
What will let's encrypt be like with 7day certs? Will it renew them every day(6 day reaction time), or every 3 days (4 days reaction time). Not every org is suited with 24/7 staffing, some people go on holidays, some public holidays extend to long weekends etc :). I would argue that it would be a good idea to give people a full week to react to renewal problems. That seems impossible for short lived certs.
What will let's encrypt be like with 7day certs? Will it renew them every day(6 day reaction time), or every 3 days (4 days reaction time). Not every org is suited with 24/7 staffing, some people go on holidays, some public holidays extend to long weekends etc :). I would argue that it would be a good idea to give people a full week to react to renewal problems. That seems impossible for short lived certs.