Haults execution until the specified mount is valid or the specified wait duration has been reached.

mount-wait.sh

#!/bin/bash 
MAX_WAIT="10"

[[ -z "$1" ]] && exit 1 || MOUNT="$1" 

if [[ ! -z "$2" ]]; then 
    reg="^[0-9]+$" && [[ ! "$2" =~ $reg ]] && exit 1  
    MAX_WAIT="$2"
fi 

seconds_waited=0 # not necessary, but prevents an env var from conflicting

while [[ ! $(findmnt "$MOUNT") ]]; do 
    seconds_waited=$(($seconds_waited + 1))
    [[ "$seconds_waited" -ge "$MAX_WAIT" ]] && exit 1 || sleep 1
done 

echo 1 && exit 0

Usage in a script:

if [[ $(mount-wait.sh "/mnt/someplace" 5) ]]; then 
      echo "Mount found!"
else
      echo "Never found a mount."
fi 

This example will wait a maximum of 5 seconds for something to be mounted on /mnt/someplace before giving up.
If it gives up, it says "Never found a mount.", otherwise "Mount found!"