The courts have generally upheld such periods as long as they are reasonable. Since the Supreme Court agreed with these decisions, in Heimeshoff, that plan-based limitations were enforceable, the courts have focused on how short can be "reasonable."
But, there is, of course, another aspect to the validity of a plan-based period, i.e., participants must know of it. And, as the courts developed the body of law in favor of limitations periods, they also required that the participants be informed of the period in the summary plan description.
A recent case took that requirement one step further. In Moyer v. Metropolitan Life Insurance, the Sixth Circuit held that the plan-based period was only enforceable against a disability plan participant if the plan disclosed the period in the letter denying benefits. The court based its conclusion on language in the DOL's claims regulation, which describes the information that must be included in a notice denying a participant's claim or appeal.
While the court's reading of the claims regulation can be criticized, it cited a lot of cases that read the regulation the same way. And, the dissent didn't disagree with the construction of the regulation as much as it challenged the majority for relying on an issue that was not raised by the participant or briefed by the parties.
Note that the reasoning of the court would apply just as much to plans that do not specify a shorter limitations period (the court's reading of the regulation is that the notice denying an appeal must state that the participant may bring a lawsuit and the period for doing so). So, all plans should review the forms of letters used to deny appeals, to ensure that they are in compliance. Such action is even more important where a plan-based period is at stake.