Script func for 'time since boot'?

Is there a script func for 'time since boot' ?
such as displayed on console in brackets such as follows:
Fri Dec 20 12:24:02 2019 kern.warn kernel: [961972.620373] ....

like to capture that value when hotplug script is called since logger calls appear to be queued until after key startup happens.

Read the first value in /proc/uptime if you want a value (in seconds) that you can use in a script.

# cut -d' ' -f1 /proc/uptime