How to add timestamp to log output entries with cron?

I am trying to schedule htcacheclean to run every half hour with cron. The service itself runs fine, but I can't figure out how to get a timestamp to append to the log entries themselves (not the cron-log filename).

I could not quite find an answer anywhere as to how to add the timestamp to log entries themselves. I only kept seeing questions and answers for how to add date timestamps to cron log filenames which is not what I am looking to do.

This is what I have in crontab -e right now:

0,30  *   *   *   *       /usr/sbin/htcacheclean -v -n -t -p/var/cache/apache/mod_disk_cache -l1M >> /path/to/cron-output.log 2>&1

Currently this is how my output is printing:

Statistics:
size limit 1.0M
total size was 167.4K, total size now 167.4K
total entries was 5, total entries now 5

Now I just need a timestamp to appear next to the log entry just before "Statistics".

Edit:

Example of what I'm trying to do:

0000-00-00 00:00:00: Statistics:
size limit 1.0M
total size was 167.4K, total size now 167.4K
total entries was 5, total entries now 5

I want to add year, month, day, hour, minute, and seconds.

Thanks ahead of time!

Solution:

I wanted to add in the full solution here as suggested by @glenn jackman.

0,30  *  *  *  *    { printf "\%s: " "$(date "+\%F \%T")"; /usr/sbin/htcacheclean -v -n -t -p/var/cache/apache/mod_disk_cache -l1M ; } >> /path/to/cron-output.log 2>&1

After adding the printf command in the cron task, this is now what my output looks like:

2018-02-05 21:10:01: Statistics:
size limit 1.0M
total size was 1009.0K, total size now 1009.0K
total entries was 24, total entries now 24

Solution

You could just use the date command in your cron entry, like this:

0,30 * * * * { printf "\%s: " "$(date "+\%F \%T")"; /usr/sbin/htcacheclean -v -n -t -p/var/cache/apache/mod_disk_cache -l1M ; } >> /path/to/cron-output.log 2>&1
# ...........^.^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^.........................................................................^^^

The printf is a bit convoluted, but it suppresses the newline like you want.

Edited to escape the percent signs. See comments below.