In a car as a tourist or in a freight vehicle importing/exporting goods ?
I suspect, but will be honest enough to say that I don't know, that customs clearance will be more than a 30 second check. Maybe if we had implemented the required infrastructure that's all it should need. Thing is we haven't.
The vast majority of shipments (98%) go through on the basis of pre-notification by registered (trusted) shippers and hauliers.
Checkout the Rotterdam website, (largest container port in Europe), handling imports from "WTO" countries.
Container seals are checked and barcodes scanned - in seconds.
Upon leaving, containers lorries drive through arches "sniffing" for dodgy substances or unexpected heat (stowaways?).
Only "red flags" get pulled over.
IIRC, Eurotunnel has around 8000 lorries per day. (4000 each way)
HMRC boss, Jon Thomson has no plans to inspect more shipments.
For the first 6 months, EU lorries arriving without pre-registration will be waived through and told what to do next time. (see website).
If 1% are inspected, that would be 2-3 an hour. Inconvenient for the truckers pulled over ( which can happen now) - but not an obvious cause of general delay.
Of course there will be some extra admin - behind the scenes - but border delays seem vastly exaggerated.
And many shippers already do import/export admin anyway - so no surprises or "cliff edges".
Lastly, even some EU shipments have admin - for EU's Intrastat.
Eurotunnel HAS implemented infrastructure.
Not only on the ET website, but one can see the many empty truck lanes by the entry gates.