Not all accident/incident requires evacuation.
Before deciding to proceed with evacuation, a number of things must be done first.
How bad was the situation?
Is a controlled disembarkation a better option? (evacuation often causes more injury)
Is the checklist done?
Are the engines still running? If so can it be shutdown from the cockpit control?
Any fire that must be extinguished first?
Remember pilot have no direct view of whats going on behind them both inside and outside.
Remember evacuate with engine running at unknown power is like sending people into shredder.
90 second is short or long to reach a decision is not for us to judge cos we are not in the cockpit and some of commenter don't even flies B777.