On boarding forms - when do you send?

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Greetings all -

Starbucks is in the middle of design sessions with Taleo for a new on boarding portal.  This is the first time we are automating this experience for new hires and hiring managers. 

We have several forms that we will be asking certain levels of new hires to sign as a part of their hire or promotion.  My question is when should those be sent?  On boarding won't be triggered until the new hire has accepted the offer.  In my mind it is almost too late to say, oh BTW, now I need you to agree to this new form (non-solicitation or confidentiality form) on your first day.  Should those continue to be sent electronically with the offer letter?  Or is it enough they are referred to as a condition of employment in