In a Skritter 1/2 hour, I study 175 - 200 items, and this take roughly 50 minutes real time. I spend a bit of time thinking about items, relearning, looking at how used etc., so presumably this is quite slow - I wouldn't mind improving this, but wondered what others are seeing on these metrics?

it all depends on yor and your way of studying.
yesterday I did 30 minutes of skritter in about 40 minutes real time.

It totally depends what you do. If I just go through the reviews with no extra thought or investigation it's not much different, but if I concentrate on reading the example sentences or something the real time can be considerably more.

Thanks - I guess the skritter/real time ratio is ok, but having tried yesterday/today, can't get the 175/200 items per half hour up much - which is a shame, as I read an older post that someone cleared a 1800 queue in 3 hours ... I could do with that clearing power!

I think it helps to mix up your study methods. Decide in advance that you are just going to put your head down and blast through, or that you are going to drill down a bit, do the dictionary lookups, read the example sentences, make mnemonics, etc. If you decide in advance that you are not going to do all the "extras" in a given session you may find some satisfaction in seeing the queue shrink rapidly. And your retention may be higher than you fear it will be, despite not having done the extras. Anyway, variety keeps things interesting.

I was wondering if time tracking on Skritter could be changed somehow? I just did 500 words in "20 minutes". Obviously, it took me much longer, but Skritter would show me just 20.

I don't care too much about that, but I was wondering what metric "Skritter time" is. As it is now, I don't see any value in metrics and I think about in doing time-tracking myself to measure "real time". What's the point in stopping the clock every time I click an answer?

as long as its for all the same its just "skritter time" with its own mystical features...

For me the time is rather accurate, because for example sometimes I could to 1 review in 2 seconds but I keep looking around, talk to people or whatever and the app counts until 30 seconds anyway.

So in sum, I think for me it's fine.