The retry time is stored in a file /var/qmail/control/queuelifetime and is a number of seconds.
# 86400 = 1 day
# 172800 = 2 days
# 259200 = 3 days
# 345600 = 4 days
# 432000 = 5 days
# 518400 = 6 days
# 604800 = 7 days
nano /var/qmail/control/queuelifetime
qmailctl restart
# 172800 = 2 days
# 259200 = 3 days
# 345600 = 4 days
# 432000 = 5 days
# 518400 = 6 days
# 604800 = 7 days
nano /var/qmail/control/queuelifetime
qmailctl restart