Hi, I have the same issue, any time I add an Initiation form, for instance having 3 simple people picker fields to get user to be used by workflow and update current item properties with the same, the workflow takes approximately 30 sec to complete the starting phase.
I have tried Dave suggestion (pause for 5 min at the very beginning of workflow) but the result is exactly the same, more 30 sec waiting system feedback.
I have noticed that the delay to obtain the landing page is significantly minor in case the form is a task form inside the workflow.
I think that there is something not properly working in the communication between Nintex Form and Workflow DB in case of an initiation form only, maybe this occurs only in some cases ....or for some misconfiguration of Form or Workflow DB.
I have also another doubt: is it possible that this dealy is due to the fact that my 3 people picker fields are updating the current item where the workflow is running? This maybe could be the root cause