Pot size should always determine the life span of a mother plant. Never let a mother plant get rootbound. Rootbound plants quickly lose their structure and new growth becomes thin and scraggly. Plan for about a month per gallon of media. I keep mothers in 3 gallon pots for 3 months max before they’re replaced. Do not wait until the mother is close to rootbound before taking their replacement. If I’m keeping a mother for 3 months I’ll take the clone to replace her when she’s at peak health at about 2 months. By the the the original mother plant is 3 months old and ready to be killed, her replacement is a month old. Never make a clone and kill the mother at the same time. Always keep the original until the backup is rooted, transplanted and healthy.