All praise is due to Allah. May Allah's peace and blessings be upon our Prophet Muhammad, his family, and all his companions.
To proceed:
The contemporary scholars have differed into three opinions regarding simultaneity and not delaying in changing similar currencies regardless of whether the currency being changed is of smaller denomination like changing a ten riyal note for ten one riyal notes, or two five riyal notes, and so on, or changing the currency to minerals (silver and gold) of a similar value.
Firstly: It is compulsory to achieve simultaneity and not to delay when changing currencies of a similar nature, changing  minerals for minerals, or currency for minerals. This is the opinion of the majority.
Secondly: Simultaneity and not delaying are not compulsory in this issue, rather, it is permissible to delay.  
Thirdly: Simultaneity and not delaying are not compulsory in this issue. However, it is not permissible to delay in this issue. This was the opinion of Shaykh as-Si'di.
The preponderant opinion is that it is not compulsory to achieve simultaneity and not delaying in this issue, and it is permissible to delay.