Checking out the block explorer and am curious about the below:
"Seen time of newest mature block Oct 10, 2015 at 8:52am (UTC)"
This obviously can't be the last found block as it's almost 4 days ago. If its the amount of time before you can spend you coinbase transaction then isn't that rather a very long time?
That date is the last mature block, or as you said the time before you can spend your coinbase.
Block times have been pretty slow lately so it may be artificially long.
Correct, it's the most recent coinbase that can be spent. It's supposed to be 24 hours, but thanks to heavy mining instability (we've got a pool that hops on and off as the difficulty adjusts), our median block time is closer to 40 minutes.