Why does a 100 watt light bulb not have a time factor?

100 watts means it uses 100 joules of energy per second.

In other words, power is a RATE of using or generating energy, and 1 watt is 1 joules per second, where the joule is a unit of energy.

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You have the common confusion between energy and power.  (It's common because science is taught so badly in US schools.)

Time isn't a factor because 100 watts is power, like horsepower.  Energy is like gallons of fuel.  You don't ask how many gallons is equal to a horsepower, do you?  You ask how many horsepower the engine was making and how LONG the engine was running, and that lets you calculate how much fuel it used.

It's the same thing with light bulbs, or hair dryers, or motors.  They use a certain number of watts in normal operation.  You multiply this by time to get the energy consumed.  You can measure this in joules, but the numbers quickly get cumbersome; electric bills are given in kilowatt-hours (thousands of watts times hours) for that reason.

If you look at your electric bill, you'll see your consumption is measured in KWH.  That's kilowatt-hours.  A 100-watt lightbulb uses 1/10 of a kilowatt, so if you run it for 10 hours you'll use 1 kWh.  Not so hard, is it?