Which crontab entry could be used to set the system time at regular intervals?

The date command with $d $t $24 syntax is incorrect for synchronizing time with an NTP server; it's used for displaying or setting local time with specific arguments.

The ntpdate command is specifically designed for performing a one-time synchronization of the system clock with a specified Network Time Protocol (NTP) server. Using ntpdate ntp1.digex.net in a crontab entry will fetch the accurate time from ntp1.digex.net and adjust the local system clock accordingly at 00:01 daily.

The date command cannot directly synchronize with an NTP server using a server hostname; it's for local time management.

runcron is not a standard command for scheduling tasks within cron, and the command structure is incorrect for time synchronization.

settime is not a standard command for time synchronization, and the arguments are incorrect for NTP.