I just noticed that there are slight deviations (about half a minute) from the timestamps my cgminer reports from the ones on Blockchain Explorers like "BTC.com".
My time settings should be fine, just counterchecked them with "time.is" and the difference is just a few milliseconds.
Anything I have to worry about? Just wanted to make sure everything runs fine. Would be sad if a found Block is rejected by the network because of a bad time stamp

That's true. On the other hand, the timestamps correlate with the data from
https://live.blockcypher.com/btc/I cannot tell which source is more to be trusted to be accurate.
In regards to the deviating timestamps I think there would only be an issue if these were the consequence of the propagation of new blocks to/from the network being too slow, potentially giving another found block precedence.
The timestamp that is used for the mining process is anyway provided by the client and added to the mined block header. If I understood the stratum protocol spec correctly, any timestamp within a 60s threshold is considered valid from the Bitcoin network's perspective.