Speed work - or are these intervals?

I didn't have long to run today so I tried some Yasso 800's. I managed to get in 4 before I thought I had better stop (I could have run another but as it was my first attempt at some speed work I thought being conservative may be best). Man! What a work out!! I feel like I have run 15kms but only ran for 30 mins. My big problem is I was running them too fast. I was trying to run 3:50'S but ran mostly 3:40's. I wonder how I am supposed to run the correct time without tripping over stuff cause I am looking at my watch instead of the footpath? Any tips would be helpful. Maybe I need to put a chalk mark at half way and then just check then....