You can use one plan to unlock more than one phone even if isn't active for the full 60 days. You have to call TracFone and transfer your plan to your second phone for it to be considered activated (it isn't enough to just put the SIM from the first phone) and the 60 days for the second phone starts from then.
Important note: You may not be able to do an online unlock for the phone that you transferred the plan from (after the transfer), instead call the TracFone unlocking department (888-442-5102) and they will unlock it (make sure to tell them the activation date if they mistakenly think you aren't eligible)