Allows the user to specify how long to hold the nodepool node. Default is 1 day. The value should be a positive integer between 1 and 99 inclusive with a one letter unit signifying how long to hold the node (m=minutes, h=hours, d=days, w=weeks, M=months). However, maximum hold duration is 1 month. Examples include: 40m, 1h, 6h, 3d, 3w, 1M.