I have poured 10s of 1000s of jigs. All molds and sizes withing molds are different. All lead is different. Most of it contains antimony or other stuff. Pure lead melts at 621°F. That being said you probaly don't have pure lead so higher heat will probably be needed.
Some things for you to do: Plug in your pot and put the mold on top of it. Put the hooks some place where they can get warmed up (base of mold, under a heat lamp, etc). When the lead if flowing freely, flux it with some candle or bee's wax. Try some pours.
If that doesn't work then you have two choices: smoke your mold with a candle or wait till warm weather. I have over 20 molds and have only had to smoke one of them. Usually heating everything up and fluxing fixes my pours.