"Worth my while" couldn't be reasonably computed until I knew more about your company, like:
-Anticipated viability of the company and revenue stream predictions
-Effort (in hours) that I would need to contribute to effect a positive outcome
-Financing model of the organization
-Compensation of other employees in a similar position to effect the outcome of the company
These things factor into the "risk", which affects the appropriate "reward". If I could make a major impact on your company by only needing to invest 8 hours per week, it wouldn't be a tough choice to make the decision to attempt to help out. If however it would take 20+ hours per week, then other things/tasks get requeued to make room to help with your startup, that changes what I would need/want to get out of it to make it worth my while...