Bikes brake more slowly than a car. I've been hit by a car while riding in the past, where they've pulled in front, overtaken and slammed on the brakes.
Sounds like a reaction time or misuse of your brakes, rather than a general rule about the amount of time required to slow the bike.
Go somewhere where there's no traffic (or obstacles), get your bike up to speed, and slowly engage the front brake. Now do it again, but more quickly. Eventually you will learn how much force you can apply without flipping the bike; this is a skill you need to ride your bike safely.
Just pulling the rear brake is not going to stop the bicycle quickly; the wheel skids and you develop no more braking force.
Sounds like a reaction time or misuse of your brakes, rather than a general rule about the amount of time required to slow the bike.
Go somewhere where there's no traffic (or obstacles), get your bike up to speed, and slowly engage the front brake. Now do it again, but more quickly. Eventually you will learn how much force you can apply without flipping the bike; this is a skill you need to ride your bike safely.
Just pulling the rear brake is not going to stop the bicycle quickly; the wheel skids and you develop no more braking force.