Welcome to the community @WayneP!
Yes that is possible. But would require some programming in a Function-Node. Something similar to what got described here:
So you could simply check the time, if it is 7 am you save a hash of the data into the static data. If it is not 7 am you would compare the hash of the current data with the hash of the earlier one in the static data. If it is not different you simply return an empty array (so it would not go on and so not post to Slack). If it is different you return the data which would run the Slack node and so post it.
Hope that is helpful!