Using the Imperfect with Pendant

Question

If pendant is used to describe past durations with a clear beginning and end, and the imperfect is used to describe continuing actions or habits in the past, why is the example "J'étais là pendant quarante-cinq minutes" instead of "J'ai été là pendant quarante-cinq minutes" since the passé composé is used to describe actions with a clear beginning & end in the past.

Is there a rule exception for using pendant and l'imparfait?

Answer

There is this pesky topic of "verbs of state", which usually ask for the imperfect tense, since they are interpreted as describing a state of being rather than an event in time. Être is one such verb, but there are others. Check here for a bit more information: https://www.lawlessfrench.com/grammar/passe-compose-vs-imparfait-2/