Just on is used in mentioning an almost exact number or amount.
[British]
Eve, squinting at the clock, saw it was just on 7 a.m.
Many were retired people, and just on a fifth were in their fifties.
See full dictionary entry for just
just on in British English
having reached exactly
it's just on five o'clock
See full dictionary entry for just
Examples of 'just on' in a sentence
just on
And were just on about mixing things up in training a bit.
Times, Sunday Times (2014)
Keeping just on the right side of twee, it succeeds in this.
Times, Sunday Times (2012)
I loved seeing my clothes on real people rather than just on a hanger.
The Sun (2015)
Most of the time people are just on their phone on Twitter and Snapchat.
Times, Sunday Times (2016)
And it has a wonderful effect on me, too, not just on these people here.
Times, Sunday Times (2007)
Cheaper house prices would draw people in, allowing young entrepreneurs to invest their money in their businesses - not just on keeping a roof over their heads.