When to mow.

I'm new to growing hay and would like some advice from the experts.  I planted hay seed last fall and as of this writing it seems as though it is doing well. It will be used to feed a few horses.  I have had two different opinions as to when to do the first cutting.  One guy said to cut when you normally would.  In these parts that would normally in June.  Hoyever another guy told me that since it a new field and the grasses are trying to establish new roots, I should let it go through Aug to make sure  a good root system gets established.  I can go with hay for awhile if that helps.  What should I do?

 

Thanks in advance.

When to mow.