API upload timing

I have recently discovered a delay in the data processing after my data has been sent to Marketo via our API. I get a portion of the data and then over the next few hours the rest of my data slowly trickles in. We are uploading all our user data at once so I am baffled by this delay. I am trying to build a nurture campaigns that will trigger off of behavior but am finding that this delay is effecting my ability to email instantaneously off a user’s action. Does anyone know how long it takes Marketo to process API uploaded data or how to speed it up?

Thanks for your help.

Terry