I found a related question What is the guidance for using "Standard Flags?" about using standard flags and custom moderator intervention flag. Using custom flag directly takes them to moderators instead of the review queue.
I have faced this situation recently on a site where I have a privilege of close voting. There was a question which was worth closing and I voted to close it. But it failed to receive one last vote for putting on hold. After a few days, close votes expired. Now, the only way is getting a mod to look at the question is flagging. So, I used custom flag and asked moderators to close the question. I can't use my close vote again because it is already used up a week ago. As usual, the flag got declined with the following reason:
Using standard flags helps us prioritize problems and resolve them faster. Please familiarize yourself with the list of standard flags: see What is Flagging?"
Now, if we think about it, what ways were left for me to make sure moderator looks at it and closes the question without using custom flag? (I have tried pinging other users in chat. Only one vote was needed).
The general procedure I heard if a question needs reopening is waiting for users to review it and if that is not successful, flag for moderators. Can this procedure be followed for closing also? If yes, wouldn't the moderator still decline the flag with above canned reason? (let's talk about performing asked action in flags later).
Also related : What do I do when I run out of flags? We can flag a question the next day when quota of flags are added the next day but this doesn't happen with the close vote. We can't use "Flagging" option because it only shows three options 1. Spam 2. Rude or Abusive 3. In the need of moderator intervention. which takes the problem again to the beginning of not using standard flags and declined with above response.