For a big fat RIS, I like to bulk age for 4-6 months. Longer if you can stand it. They aren't going to be great until 9-12 months anyway so if you have the carboy space that is where I would do it. You may also get a more consistent batch this way vs bottles.
The only concern with a long bulk age in secondary is oxidation. I like to put a CO2 blanket on top (from my kegging setup) and then seal it up good with an airlock. Just have to remember to top up the airlock every month or two.
Primary #1: Hidden Lake Nut Brown #2: Apple Cider
Secondary #1: Berry Rhubarb Wine #2: Black Currant Wine
Kegged: Cascadian Dark Ale, Orange Pale Ale IV
Bottles: Spruced Winter Warmer, Surly Bender clone, Big 50 Barleywine, Framboise Lambic, Dark Belgian Strong, Kicked by a Moose Scotch Ale, Russian Imperial Stout, Sparkling Elderflower Wine, Barolo Wine, On Deck: 2H IPA III