user-1: 
In alpha software prior to Bitcoin's release, the target interblock interval was 15 minutes, and it was reduced to 10 minutes for release.

https://www.reddit.com/r/Bitcoin/comments/56nk94/on_chain_scaling_with_schnorr_signatures/d8lmwco
Where can I find this alpha version for research?

user48884: Cryddit on Bitcointalk posted some source code that Satoshi supposedly emailed to him. This code contains a target interval of 15 minutes rather than 10. It is in https://bitcointalk.org/index.php?topic=382374.msg4108739#msg4108739. Search for nTargetSpacing.

-1: <blockquote>
<p>In alpha software prior to Bitcoin's release, the target interblock interval was 15 minutes, and it was reduced to 10 minutes for release.</p>
</blockquote>
<p><a href="https://www.reddit.com/r/Bitcoin/comments/56nk94/on_chain_scaling_with_schnorr_signatures/d8lmwco" rel="nofollow noreferrer">https://www.reddit.com/r/Bitcoin/comments/56nk94/on_chain_scaling_with_schnorr_signatures/d8lmwco</a></p>
<p>Where can I find this alpha version for research?</p>
 48884: <p>Cryddit on Bitcointalk posted some source code that Satoshi supposedly emailed to him. This code contains a target interval of 15 minutes rather than 10. It is in <a href="https://bitcointalk.org/index.php?topic=382374.msg4108739#msg4108739" rel="noreferrer">https://bitcointalk.org/index.php?topic=382374.msg4108739#msg4108739</a>. Search for <code>nTargetSpacing</code>.</p>
