Terraria Meteor has been “spawned” but isn’t anywhere in the game/world

During the day which consists of 15 minutes, when a shadow orb has been smashed that has caused no other events there is a chance of 1 out of the 50 on every second that a meteor can be enabled.

If a meteor has been configured it will spawn in the middle of the night which consists of 9 minutes, so it will spawn 4,5 minutes into the night. It spawns as follow:

1. There must be an active player (on a server), so that it is aware of the Meteor drop.

2. There should be less than a certain number of meteor tiles (small world: 401, medium world: 601, large world: 801), or the Meteor is not eligible to spawn.

3. The meteor will land within 672 blocks to each side of the spawn, so that it's close to the player.

4. A maximum of 100 attempts will be made to land the Meteor in a place where it is eligible:

   1. It may not land 50 blocks close to the borders of the map.

   2. It may not intersect with a Player, a NPC or a Chest.

   3. The top most solid block will be tried.

5. Drops will be stopped, tiles will be killed and meteorite tiles will be placed.

Now is the question, is the wooden platform a solid block?

Yes, a wooden platform is considered solid, and also has a solid top property. Water only flows through objects that have solid tops, but this doesn't happen for meteorites which check if the object itself is solid. Other items that have this effect include workbenches and tables...

Below 100 from the top they will always stop meteorites, between 50-100 only by a chance.

Taken from an answer to this question:

During the day which consists of 15 minutes, when a shadow orb has been smashed that has caused no other events there is a chance of 1 out of the 50 on every second that a meteor can be enabled.

If a meteor has been configured it will spawn in the middle of the night which consists of 9 minutes, so it will spawn 4,5 minutes into the night. It spawns as follow:

1. There must be an active player (on a server), so that it is aware of the Meteor drop.

2. There should be less than 801 meteor tiles, or the Meteor is not eligible to spawn.

3. The meteor will land within 672 blocks to each side of the spawn, so that it's close to the player.

4. A maximum of 100 attempts will be made to land the Meteor in a place where it is eligible:

   1. It may not land 50 blocks close to the borders of the map.

   2. It may not intersect with a Player, a NPC or a Chest.

   3. The top most solid block will be tried.

5. Drops will be stopped, tiles will be killed and meteorite tiles will be placed.

So there is no time requirement - if a meteor has been chosen to spawn, it will spawn in the middle of the next night. It seems you've just gotten unlucky with your meteors.

All credit for the research goes to Tom Wijsman