I updated the documentation and added a new feature.
If this is not wanted I´ll close this and only make a PR with the updated documentation.

Here the text from the comments:
2024-02-05 - Added the option to get a single value of a field or all values of a channel at a certain time (not only the last entry)
Examples:

Single channel:
sendtohttp,api.thingspeak.com,80,channels/1637928/fields/1.csv?end=2024-01-01%2023:59:00&results=1
=> gets the value of field 1 at (or the last entry before) 23:59:00 of the channel 1637928

All channels:
sendtohttp,api.thingspeak.com,80,channels/1637928/feeds.csv?end=2024-01-01%2023:59:00&results=1
=> gets the value of each field of the channel 1637928 at (or the last entry before) 23:59:00