Liam is helping his dad put away $40$ building blocks that are scattered on the floor. Liam's dad manages to put $4$ blocks into the toy bin every $30$ seconds, but each time immediately after those $30$ seconds have elapsed, Liam takes $2$ blocks out of the bin. How much time, in minutes, will it take Liam and his dad to put all $40$ blocks into the bin for the first time?