If shadowing or volunteering are going to get in the way of grades or adequate DAT preparation, then yes, cut back. With few exceptions, volunteering is icing on the cake. Make sure you have a decent cake (grades/DAT) before anything else.
As for shadowing, the vibe on here is 50-100. Look into your schools of choice to see if they're one of the special ones who have a strict required number of shadowing hours.
When you apply, you can leave the end date open for volunteering and shadowing and just put what hours you have if they are indeed on-going.