If you remove a client from a policy, then when you re-add it... NetBackup thinks the client is a new client in the policy, and if the next due backup is an incremental (differential, or cummulative) then that incremental backup effectively runs as a full.
FYI - removing clients and re-adding them also disrupts the collection of TIR information, and so will very likely also cause issues if the next scheduled full backup is a synthetic full. I realise that this particular point is not relevant in this situation, but worth highlighting again.
FYI - again not relevant in this particular case - but worth re-iterating is that... renaming client in a backup policy has the same effect as deleting/removing it, and re-adding it - and so has the same effect as the points above.
Martin's use of the '-ut' switch indicates that you would be using a 'universal time', but you can use a standard datetime if you want:
-offline -onlineat MM/DD/YYYY:HH:MM:SS
-offline -onlineat "MM/DD/YYYY HH:MM:SS"
