The Uptime & Line Uptime not accurate in openwrt 18.06.1

my router
TP-Link W8970 ver. 1.2
openwrt 18.06.1
When I turn on the device For the first time get
Uptime = 2m 00s etc From the moment of router is run !
then the router connect to the internet get
Line Uptime = 1m 38s From the moment of connect to the internet
all from now is the good
the after 1 day for ex.
check the
Uptime & Line Uptime
found this
Uptime = 18h 26m 45s
Line Uptime = 18h 0m 13s
The difference 26m but the internet in not disconnect or not loss any connection is Always connected !
and it is connection after 38 seconds from startup time why now the difference is 26m ??????

If you're referring to your WAN, you need to ask your ISP - as the control the far-end of the link.