90 secs from when??
Checklists have to be run prior to evacuation. Certainly in my experience,
Coupled with the undoubted shock of having piled in and watched your landing gear overtake you, I think 90 seconds is entirely plausible.
In my experience, Boeing evac checklists are shorter than Airbus ones, but unless someone has evidence of Asiana's SOP's regarding evacuation, I see it entirely wrong to start criticising the flight crew for this relatively short delay.