Maybe I missed something somewhere but the man page hobbit-mailack says the default delay value = 1 hour (60m). Whenever users use email ack a Hobbit alert message, the default delay appears to be 30 minutoes. I've compared these log entries to those where I have specifically set the delay to 24 hours.

1119545832 766480 1440 766480 np_filename_not_used tucdbp254.msgs yellow =20\nAcked by: "userlast, x" abc at xyz.com 1119625520 727328 30 727328 np_filename_not_used vsifed00.cpu red =20\nAcked by: "Another, First" abc at xyz.com