You found the solution, but in case you want to change the SNMP timeouts anyway, this is the right rule for that:
With the default settings checkmk tries six times in total (one attempt and then 5 retries) with a timeout of one second each to gain the data. Overall, this takes approximately 6 seconds. Some devices work better with different settings, e.g. 3 times @ 4 seconds or whatever. It’s a bit of trial and error.