At 3rd level, a mauler familiar gains the Battle Form ability:
Battle Form (Su)
At 3rd level, a mauler gains the ability to transform into a larger, more ferocious form and back as a standard action three times per day. In battle form, the mauler’s size becomes Medium and it gains a +2 size bonus to its Strength score. Since many familiars are Tiny or Diminutive, be sure to check for any additional Strength and Dexterity adjustments for increasing in size from Tiny or Diminutive to Medium. This is a polymorph effect.
Is there a time limit to stay in Battle form? Can he stays in Battle Form all day?