It is just a cap over the same vent. Doesn't matter if it is there or not. It will still vent properly through the vent aperture. It is just an opening to allow steam to escape from inside the cooking chamber, not a "precision engineered" vent of a critical size. The small holes in the inner metal lid are more important in the exit of steam from the cooking pot.

You don't need a timer, the rice cooker switches off automatically when the rice is cooked. (drops back from "cooking" level of heat to a low "keep warm" setting.)

Below the inner pot is a sensor that detects when all the water in the pot has been fully absorbed by the rice. Once all the water is absorbed, the pot starts to get hotter quite quickly, this is detected by the sensor and the little switch flicks back up to "keep warm" position.

The rice is NOT yet ready to eat at that point, it still needs to sit on the "keep warm" setting for 10 to 15 minutes for moisture in the outer part of each grain of rice to slowly absorb into the centre.  This extra little wait is the difference between "OK" and "delicious" rice.

I don't know if you have used rice cookers before - you have to get the balance of water to rice just right. You will probably have a bit of trial and error the first few times you use it. If the rice is too hard and sticks to the pot, add a little more water next time. If the rice is too soft and mushy, use a little less water next time. Adding a SMALL amount of cooking oil, maybe 1 teaspoon, to the pot at the beginning helps to stop the rice foaming up during cooking. Always wash the rice first in several changes of water before cooking it - this prevents a sticky goo forming that will stick to the base of the pot. (rice grains usually have a fine coating of "rice dust" over them, washing this off makes for much better cooked rice.) Keep rinsing the rice till the rinse water is clear, not cloudy.

Different types of rice will need a different proportion of rice to water, so you will need to experiment to find the right balance for the rice you use. My favourite is extra long grain Basmati rice, grown in Pakistan. It is aromatic and keeps grain separate, it doesn't go mushy. (The good stuff doesn't, any way...) Some cuisines prefer slightly sticky or softer rice, not my preference...

These Japanese-made rice cookers are the best. I don't know why, but they just seem to cook better without burning or catching on the bottom.

Good luck with it.