In Davis v. Abington Mem. Hosp. (precedential opinion here), the Third Circuit addressed the level of specificity required in a complaint. Allegations that an employee "typically" worked a 40-hour week and "frequently" worked hours outside of her shift or during meal breaks, standing alone, are not enough to state an overtime claim. The employee must specify that she worked 40 hours in a week, and then worked extra hours beyond 40 in that week.
Even with this requirement, the pleading standard is hardly demanding:
[W]e do not hold that a plaintiff must identify the exact dates and times that she worked overtime. For instance, a plaintiff’s claim that she “typically” worked forty hours per week, worked extra hours during such a forty-hour week, and was not compensated for extra hours beyond forty hours he or she worked during one or more of those forty-hour weeks, would suffice.The Third Circuit noted that this issue has "divided courts around the country." So if you're outside of the Third Circuit, check for local precedent on this issue.