If you have 60 separate :#channelname: entries, one for each channel name, that could work assuming you aren't joining all 60 at the same time. If your timer command contains words beginning with % or $ you would want to put them inside $unsafe() to delay their evaluation until you joined the channel.
You can also test whether this message appears in both channels:
/msg #channel1,#channel2 test
and whether the status window output from "/version" (not $version) gives an indication what is the max number of channels this works for. The length of the list of channels also limits the length of the message, so even if it lets you use 20 channels in 1 message, you'll need to test if that shortens the size of the message that's visible in channels.