Applying for rebates vs. actual Install of NAV

I know this is a silly question but here goes anyway:

                       Today, in order  to take advantage of a local retailer's/Mfg 'promotion' 's time-constraints (i.e.' purchase-proof-date' + rebate application 'mail by' date) I purchased NAV ISS2009.

                       However, my current Trend Micro ISS 2008 doesn't expire until August 8th,2009 !  

                       Can i wait until my T.M. expires and then  install the Norton even tho i will have applied for the NAV 'rebates' prior to Aug 8th's expiration of T.M.?  (i hope you're not laughing at this question)      :)   Thanks in advance....Edythe