Designer As Consultant for Startup - Collaboration Models?

Another question regarding a prepaid retainer of let’s say X hours. Do you think it is advisable to break down the hours to the specifics actions that are expected to consume these X hours? For example A hours research B hours teleconference etc. or just sell a package of X hours to reach, what I consider, a minimum fee amount I consider as worthwhile in order to sell them my contacts, experience on their domain and skills?
I am mostly inclined to this direction. An open retainer billed in the end of each month, eventually for this type of projects I think is not favorable as I have no commitment from their side of collaboration and I will eventually may need to sell skills for just a couple of hours that I am not willing to do so.