A probationary employee with questionable attendance

I hired a new employee a month ago.
I am not their direct mentor—a junior colleague is—but after the 3-month probationary period and a performance review,
I have to report to the team leader to decide whether to retain them.
This is a young person's first job; they have a bright and friendly personality, and
while they aren't ready to handle main tasks yet, their comprehension during training
seems quite good, and they even try to find side tasks or offer help on their own.
The one thing bothering me is their attendance; it's not outright terrible, but it's ambiguously poor.
They were about 5 to 10 minutes late a few times during the initial period, and after my junior colleague gave them a warning,
they apologized and stopped being late, but now they arrive right at the limit, around 8:57–8:59 AM.
Also, after going out for lunch, they return every day right at 1:00 or 1:01 PM.
They are a smoker (I am a smoker too, so I take breaks as well), but they step away from their desk quite frequently.
When the junior colleague checked, they laughed and said the employee steps away about 6 to 7 times (for 10–20 minutes each).
Aside from this, they show initiative and seem fine, but since most of our work involves collaboration on projects with at least two or more people,
I am worried about whether this will cause issues in teamwork.
To be honest, I'm not sure. Would this ambiguous attendance affect collaboration...?
It would be easier to fail their probation if their attendance was clearly bad,
but this subtle pattern is slightly bothering me.
Hmm... I'm posting this because I'd like to hear various opinions on what you all think.