Well yes, I know, and I'm always faster doing 50 as 2x25 instead of a straight 50, but if my time for a straight 50 is 84 seconds, and my time for 25 is 27 seconds, that's a big difference. I'm losing around 30 seconds per length. If I pan it as hard as I can over a 50m length, I can do it in about 72s, so I'm still losing 20s per length.
I did a km of 40x25 today and my average was about 80s per 50m, which is about normal.