Going to brew two batches this weekend on two different days, both in the mid .050’s.Want to make a starter for both, different yeast. One flask and one stir-plate. What would you do?
Start one today or tomorrow. Let it make yeasties overnight, transfer to a sterilized gatorade bottle or similar and place in fridge. Start #2 same process. Cool and let sit in fridge. Take out morning of brew day, decant and let warm. Add some water, swirl and pitch. Then have a homebrew… 
How big of a flask? According to Mr. Malty, a 10 gallon batch ( 2 x 5 gallons ) at 1.050 on a stir plate would require a 1 liter starter with 2 vials. I don’t see why you can make a starter, pitch half and then save the rest in the fridge for the next day.
Are they both ales and are you using the same yeast for both? This would be a good solution…
Didn’t want to quote myself. Just read again that it was different yeast. I go back to my original post in that case…
Whoops…missed that :
In that case, depending on the yeast i would do a starter for the first day, brew early and pitch. Get the starter going for the second day and pitch later on the 2nd day. I pitch my starters at high krausen usually, so in the 18-24 hour range. So if you pitch on day 1 at noon or so, you should have plenty of time for day 2 starter to get to be ready to pitch in the afternoon.