We roasted our bulbs for 60 minutes to get a soft paste consistency. Depending on your desired consistency, you can roast the garlic for closer to 40-45 minutes as well. The bulbs are done roasting when they are golden on top and easily pierced with a fork or knife.
The olive oil helps retain moisture so the bulbs don't end up dry or brittle. Simply drizzle it on top of the cut side of the bulbs before roasting.