I maintain a public bitcoin-data/block-arrival-times dataset with timestamp of block arrival times collected across many different nodes.
Feel free to use the dataset - and if you happen to have timestamps that you can share, feel free to contribute them.
Just added 90k block timestamps from six peer-observer nodes each in https://github.com/bitcoin-data/block-arrival-times/pull/25. This means, we now have more than 10 years of coverage for block arrival timestamps (from multiple sources). 
The dataset now has a dedicated GitHub pages website providing an overview over the dataset contents and hopefully helping a bit with SEO:
I invite everyone reading this to contribute their timestamps to the dataset! 
