Just to add a perspective from another jurisdiction:
In Germany, the general definition of "work time" is:
Arbeitszeit im Sinne dieses Gesetzes ist die Zeit vom Beginn bis zum
Ende der Arbeit ohne die Ruhepausen; [...]
Arbeitszeitgesetz (ArbZG), § 2
Work time as used in this law is the time from the beginning to the
end of work, excluding breaks; [...]
Following that definition, the whole time from when you start work to when you finish is work time - no matter what you actually do during that time.
Your employer may tell you to sit quietly on your chair and do nothing, or you may have to participate in a fire drill, or you may have to wait for the phone to ring to provide customer service - it all counts as work time.
So yes, the fire drill counts as work time. It does not matter whether the employer wanted to perform the drill or not - once the employee has started work, the "risk" (called ''Betriebsrisko'' in German law) of the employee not being able to work properly for any reason (no work available, electricity failing, fire drill...) is on the employer.
In addition to that:
Even if you could not work for a whole day (e.g. office is flooded, or power outage), you still need to be paid. This is regulated in § 615 BGB:
Kommt der Dienstberechtigte mit der Annahme der Dienste in Verzug, so
kann der Verpflichtete für die infolge des Verzugs nicht geleisteten
Dienste die vereinbarte Vergütung verlangen, ohne zur Nachleistung
verpflichtet zu sein. [...] Die Sätze 1 und 2 gelten entsprechend in
den Fällen, in denen der Arbeitgeber das Risiko des Arbeitsausfalls
If the recipient of a service defaults on accepting the service, the
provider of the service may demand the agreed-upon fee for the
services they could not render, without being obliged to render theses
services later. [...] Sentence 1 and 2 also apply in cases, where the
employer bears the risk of a work outage.
According to decisions by the highest court (BAG) this means that the employer bears the risk of an employee not being able to work, unless this is caused by the employee themselves (such as by being absent or ill). If an employee cannot work for a different reason, they still need to be paid, and do not have to make up the time later. However, these general rules can be modified in work contracts or general agreements (''Tarifvertrag'') to impose some liability on the employer.
This actually occurs in practice, for example if an employer must temporarily shut down operations due to natural desasters or technical problems - the employees must still be paid. Note, however, that this only applies to situations where the employee is available for work - if the employee cannot come to work, for example because of snow, they need not be paid.