Great Question! If a delay or shortened schedule still allows for enough meaningful instruction and interaction (e.g., consistent routines, opportunities for teacher–child interaction, and typical instructional practices), an observation may still provide valid data.
However, if the day looks very different from a typical classroom experience (assemblies, testing schedules, weather-related supervision routines, limited instructional time, high student absences, or frequent transitions), it may be better to reschedule. Observing on an atypical day risks collecting data that doesn’t truly represent the classroom’s average experience.