Lazy G -- there are of course times when no othermethod will work but to sync the donors together.
I might suggest that you do what you asked, try getting them all to cycle at once, then on thier next heat they will at least be all within a day or two of each other. When we start the donors on injections -- you can get by with using day 9 - 10 - 11 - and even 12 at the latest. The KEY is to make darn sure EVERY one has a good functioning CL - a CL that has not gotten the signal to start regression yet, or they will not work.
I never use day 8, and the only donor that I can remember having to use day 13 failed to respond to treatment.
I preffer day 11 on cows, and day 10 on a hfr (IF I ever agree to do one -- might be best you don't ask that favor -- I decline when ever possible and succeed MOST of the time to get out of it! hehe)
In your case -- your donors could cycle over a 3-4 day period on thier second heat and you could still do them all together. The beauty of having the donors as residents is this -- I never have to worry about trying to go and do 3-4 or more donors in one day. I schedule plenty of time to do the flush on time, work in the lab with no hurry. It works extremely well for me. Not that we can't do more than one, but it prevents the first eggs flushed from having to sit and wait on the last ones. There is a time frame where it gets counterproductive if they sit too long. Normally speaking, we try to have all embryos in the freezer by 2 hours from colection.
In your case, you may have to try and flush a couple -- process -- flush a couple more etc.
If you wait too long to do the flush on day 7 -- then your resulting embryos get too big -- they grow VERY fast past the day 7 time -- those at 7.5 would be about 2 grade stages older already. Easily fixed by simply starting 1/2 the cows at night, the other half start in the next morning. Flush the PM started cows first, the AM started cows last. Problem solved.
Any thing else I can do for you -- just ask -- we are slow here now so I have extra time any way -- in fact I just got in from going out for a 2 hour ride with my son, we love our Quarter Horses too!
Take care -- Terry
PS -- Hey Knabe -- as I mentioned, all you have to do is invest in Nebraska range land -- problem solved for distance! Your and every one else are most welcome here -- I can see me working for a Co-Op!! hehehe