A job costing time clock does two jobs at once: it records that someone worked, and it records what they worked on. The second is where these systems succeed or fail, and the reason is almost never the hardware.
The job list is the product
A clock can only allocate to codes somebody maintains. If the list is stale, staff pick the nearest plausible code and your costing is confidently wrong. Decide who creates a job code, who closes it, and what happens when work arrives before the code exists. Most failed implementations are a list nobody owned, not a device that could not capture the input.
Make switching jobs faster than not bothering
If moving from one job to another takes four screens, people will clock the whole day to the first one. A short code, a recently used list, or a scan at the point of work all remove the friction. Watch a real shift change before buying, because the difference between a three second switch and a twenty second one decides whether your data means anything.
Reconcile costed hours to paid hours every period
Total hours allocated to jobs should equal total hours paid, less an explicit bucket for non-productive time. If they do not match, the gap is being absorbed somewhere and your job margins are fiction. Run that check every pay period rather than at year end, when nobody can remember what happened in March.
Pay rules and costing rules are different questions
Overtime is paid under your jurisdiction's rules regardless of which job it was worked on, and how you then allocate that premium across jobs is an accounting policy you choose. Write it down once. Systems that quietly allocate the premium to whichever job ran late will distort exactly the jobs you most want to understand.
Questions people ask about job costing time clock
Can a standard time clock do job costing?
Some can with a code entry step, but the useful ones keep a maintained job list and report hours by job rather than only by person.
How granular should job codes be?
Granular enough to change a decision, no finer. Codes nobody reports on cost entry time and return nothing.
What about time that is not chargeable?
Give it explicit codes. Forcing everything onto jobs is how non-productive time disappears and margins look better than they are.