There is no etiquette with DC cabs. Don't even try. Your wait time charge is issued by law as noted below. Don't be surprised if the driver also tries to charge you an additional dollar or two for making the stop on top of the wait time.

Wait time charges shall apply as follows:
a. There shall be no charge for wait time up to four (4) minutes and
fifty-nine (59) seconds;
b. From five (5) minutes up to nine (9) minutes and fifty-nine (59)
seconds, the charge shall be two dollars ($2.00);
c. From ten (10) minutes up to fourteen (14) minutes and fifty-nine
(59) seconds, there is an additional charge of one dollar and fifty
cents ($1.50); and
d. If the wait time reaches fifteen (15) minutes, the entire charge shall
convert to the twenty-five dollars ($25.00) hourly rate, reflected in
Appendix 8-2, Taxicab Zone Map, prorated as six dollars and
twenty-five cents ($6.25) for each fifteen minutes (15) minutes or
quarter hour. Fractions of a quarter after the first fifteen minutes
(15 minutes) shall be charged the full quarter hour charge of six
dollars and twenty-five cents ($6.25).

Allow me to add this wager: I bet the driver will tell you he waited longer than you actually did. If you were 16 minutes, I'll bet he'd try to tell you it was 31.

For all those who hate DC cabs, we may have an opportunity to do something about it. Consider attending (.....ing and moaning?) one of these public hearings on DC taxicab service and giving them an earful.

The ONLY solution is meters. There will be no other way to stop the nonsense and the cheats.