ezmlm-make -d dir dot local host
and add a line to your crontab file:
30 04 * * * ezmlm-get dir
and execute crontab(1). This will generate a digest each day at 04:30 am. In addition, a digest will be generated at any time when the latest post makes it more than 30 messages or more than 64 kbytes of message body since the latest digest. If you do not want these extra digests, edit DIR/editor and remove the ezmlm-tstdig(1) and ezmlm-get(1) lines.
If you do not need the digests to go out at a particular time, use the standard setup, but edit DIR/editor to put -t 24 on the ezmlm-tstdig(1) line instead of the default -t 48 for 48 hours. This is even easier. You can modify all parameters by editing ezmlmrc or by using the ezmlm-make(1) -4 argument when creating/editing the list. This is described in the ezmlm-make(1) man page, and the options etc, are described in the ezmlm-tstdig(1) man page.