Make sure you always use dried herbs, any moisture in fresh will make your oils mold. When I cold infuse, I keep the oil on a shelf in the house out of sun. If I was going to hot infuse, I would use a water bath for a few hours. The few times I've tried using the sun, it made the oils smell weird.
I've never had luck infusing rose petals. In fact, I just dumped a jar of weird smelling oil that had rose in it for the last couple weeks. Maybe it was the kind of rose I used, I don't know. I really need to harvest some wild rose petals and try again.
I've kept infusions around for a year or more. If there is ever any weird smells or cloudiness, toss it.