What is the longest time I can have a BPA for? I keep hearing 5 years but I have not found that anywhere. DFARS 216.703 says five years for BOAs specifically, but that's all I can find.
The answer to your question is in the FAR and depends upon whether the BPA is a multi-award or a single award, see below. In either case you would need to consult your PCO, legal, and policy offices where you work to determine how they interpret the actions that would be required for you to exceed the 5 year period for a multiple-award BPA, if that's what you are using. If it's a single award BPA then the FAR says you may not exceed one base year and four 1 year option periods.
FAR 8.405-3(d)(1) states, "Multiple-award BPAs generally should not exceed five years in length, but may do so to meet program requirements."
FAR 8.405-3(d)(2) states, "A single-award BPA shall not exceed one year. It may have up to four one-year options. See paragraph (e) of this section for requirements associated with option exercise."