How to insert : and - into timestamp string from IoT device?

I have an Arduino IoT device which reads data from an electricity meter and posts to a website database through a web call to a php script on my webserver. THis works fine and the timestamp gets into the database as expected. However it is hard to read so I want to add separators before storing onto the database. The timestamp retrieved from the meter looks like this example: 221216085802 It is sent by adding parameter &timestamp=221216085802 to a get call to the php script. In php on the webserver before I store it into the database I want to convert it to a more readable format so it looks like this: 22-12-16 08:58:02 How can I do this in php code? I.e insert two - one space and two : into the string at given positions -- Bo Berglund Developer in Sweden