Makes perfect sense, thank you very much!

Thanks for the answers.
The goal of this classification is to see how many blocks arrive on any given day on average.
I know it's a block every 10 minutes but sometimes more, sometimes less.

The timestamp is closer to reality, the median time gives a time of about an hour prior.
My problem really is because sometimes a block would give a time that is in the next calendar day, and a subsequent block would give a time that is in the day prior...
So a few consecutive blocks can have dates like so: 23/06-23/06-24/06-23/06...

I'm leaning towards using the timestamp as it's closer to reality, although I find it annoying that some blocks will end up being counted towards another day because miners are setting the time too far in advance.

Hi all,
I'm compiling some statistics about the arrival time and I was surprised to find that the timestamp included in block n+1 can sometimes be earlier than that of the preceding block n.

The wiki in https://en.bitcoin.it/wiki/Block_timestamp says it's ok:

So we have 2 times in a block: the miner timestamp, and the median time.
I want to classify these blocks by date, but depending on whether I choose the timestamp or the median time, the dates can be different (see below)

Height   Timestamp                   Median time 
17898   23/06/2009 23:19:42    23/06/2009 20:34:45
17899   23/06/2009 23:32:39    23/06/2009 21:05:33
17900   24/06/2009 00:12:58    23/06/2009 21:40:41 <--
17901   24/06/2009 00:35:19    23/06/2009 22:25:33 <--
17902   24/06/2009 01:04:59    23/06/2009 22:57:21 <--

My question is: which one would you choose?
If say you wanted to count the number of blocks on the 23rd, would you go with the timestamp or the median time?