PiLA placements are generally for 12 months (in a few cases, 10). PiLA's partners need to be able to plan ahead, and do not want to invest in training someone who will not be present long enough to make a meaningful contribution. Think of the fellowship as a fulltime job to which you commit for the full contracted period; this is not a situation where a fellow can come and go at will. Holiday, vacation, and sick day policies are generally identical to those for full-time staff at the partner organization.
PiLA fellows commit to serve for the full fellowship term. It is unacceptable to leave a placement early (except in cases of emergency evacuation due to serious illness or injury, major natural disaster, or massive political upheaval).
PiLA expects full transparency from applicants regarding other options they may be pursuing, and this should be noted in the initial application. For instance, Fulbright programs in Latin America typically begin in March. Hence, it is impossible to accept a full-term PiLA fellowship and Fulbright in the same year. PiLA fellowship offers typically come before a finalist has heard from Fulbright, so it is imperative to be very clear about one's priorities. One may apply for both, of course, but opting for one will necessitate declining the other.
There is no problem if one declines a PiLA fellowship in order to accept a Fulbright or any other opportunity. One can simply reapply to PiLA the following year, as a stronger candidate by virtue of their additional professional experience.