The thermocycler handles the part of PCR that looks like it needs timing. Everything that actually goes wrong on a busy afternoon happens before the lid closes or after it opens.
Before: the clock you are not watching
Setup is not timed in the protocol, and it is where the timing errors live. Thawed primers and polymerase have a window. Master mix sitting at room temperature while you take a phone call has a window. Neither has an alarm attached, so both are governed by whether you happen to remember.
The fix is to start a timer when the reagents come out, not when the run starts. Name it after the reagent, give it the window you are prepared to accept, and let it be the thing that interrupts you rather than your memory.
During: do not babysit the block
A thermocycler run is the one part of this that genuinely does not need you. The useful timer here is not the run itself but the thing you intend to have ready when it finishes — the gel poured, the plate labelled, the next set of samples thawed.
Set that timer to end a few minutes before the run does. A run that finishes into a prepared bench is a different afternoon from one that finishes into an empty one.
After: the short windows
Downstream is where several short, overlapping timings appear at once, and where a single-timer workflow breaks. Loading, running, staining and imaging each have their own duration, and at least two of them will be in flight simultaneously if you are running more than one gel.
- One named timer per gel, not one per step — "gel A run" is more useful than "45 min"
- Start the stain timer when the gel goes in, not when you get back to the bench
- If a product is going into the fridge rather than straight onto a gel, the timer that matters is the one telling you it is still there tomorrow
Why this is a timer problem and not a protocol problem
None of these durations are unknown. They are all written down somewhere. The reason they go wrong is that they overlap, and a protocol is a list while an afternoon is a set of things happening at once. Timers are how a list becomes a schedule.