I should also point out as a parachute pilot myself, we are not operating under IFR when dropping. We are operating under an exemption that allows us into Class A airspace. It is physically impossible for us to operate under Instrument Flight Rules when climbing and descending vertically!! So in anwer to the original question relating to parachute dropping none of the time is IFR. You will of course be climbing and descending through cloud a lot of time so you can log those bits in the instrument flight column.
SNS is bang on with his interpretation. At work we fly a mix of IFR and VFR and I have only ever logged flight time by sole reference to instruments not IFR time. I make a note in the comments column if it was an IFR or VFR flight plan. I can often do an IFR flight and not see so much as a fluff of cloud in 6 hours.
In the UK a pilot with a PPL and no IR or IMC can fly everywhere under IFR having to remain VMC so logging IFR time is utterly pointless.