Timeoffset with vertex animation toolset

I have created a big crowd animation with instanced meshes and then animated the people with the vertex animation toolset. But how can I time off-set the individual crowd members? I have used the “per instance random” node to randomize their colors and small variances in size and rotation etc. I have also used this technique to randomize their speed, but how can I randomize the animation “current time” to make them all look even more like they are moving individually?