whether you are using hop bags or simply tossing them straight in, typically the hops are left in for the entire chilling process. this is primarily the aroma and flavor addition and will add no detectable bitterness, no matter how long they are left in the wort while chilling (especially in a DIPA).
hope this helps. cheers.
primary: -one-shot IPA; -dogs of war DIPA; -utmost corner DIPA
kegged: -flattering glass west coast american amber ale; -dogs of war DIPA (5); -brown in hue double brown ale
bottled: -dogs of war DIPA (4); -all-simcoe one-shot IPA; -with mirth imperial red ale; -one-shot IPA (3); -gambold robust christmas porter