... How earlier? How big of a shot glass and how big are the containers? Thought it doesn't really matter, there is no sense being fussy about watering or giving a little bit at a time or whatever. There is no need to fear over-watering. That is caused by a lack of oxygen in the rhizosphere, usually due to a poor (compact) medium, but this doesn't happen in two or even three successive waterings. In a properly amended medium the problem is when the containers are constantly sitting in stagnant water.
The easiest thing to do is something like this... don't try to measure precisely how much to water seedlings (or any plant). Water until the medium is fully saturated, until you see some run-off. When you pick up the container you'll feel it is rather heavy. Given time the water will evaporate and\or be taken up by the roots if they have grown in. Seeds don't need to be watered as frequently as a seedling a couple weeks old. But, given time you will see when the medium has mostly dried out, and when you lift it it will feel much lighter: it is time to water again.