Mine nearly drained the battery the first time I fired it up after a long time off the road but caught just in time. In normal use it's more or less instant. Have you checked your fuel filter? Maybe a blocked breather in the fuel cap?
I find mine likes the choke being used in most starting conditions. Pull the choke out and then give the twist grip a slight turn, if the choke starts to slip back in you have given the twist grip too much. Then try turning it over.
Mine has had a tendancy to flood if you get it wrong and then you have to leave it to settle down for a while before it wants to fire again.