If "MaxElapsed" is greater than or equal to 0, there's no limit in MaxElapsed.
Else, if there's a limit (if MaxElapsed is greater than 0), will be the max amount in seconds of time elapsed while being offline. This means that if I had not connected for 3 weeks (27 days) but MaxElapsed is 12 hours, once I join I will only mine 12 hours while being offline, then it will apply the penalty. If there's no limit, in this case I would mine 27 days and then apply the penalty.

old config.yml mineCryptoOffline:

mineCryptoOffline:
Register: true
Penalty: 0.02

new config.yml mineCryptoOffline:

mineCryptoOffline:
Register: true
Penalty: 0.02
MaxElapsed: 86400