For conventional concrete mixtures at laboratory temperatures
of 68 to 77°F [20 to 25°C], make the initial test after
an elapsed time of 3 to 4 h after initial contact between cement
and water. Subsequent tests should be made at 1⁄2- to 1-h
intervals. For concrete mixtures containing accelerators, or at
temperatures higher than laboratory, it is advisable to make the
initial test after an elapsed time of 1 to 2 h and subsequent tests
at 1⁄2-h intervals. For concrete mixtures containing retarders, or
at temperatures lower than laboratory, the initial test may be
deferred until an elapsed time of 4 to 6 h. In all cases, time
intervals between subsequent tests may be adjusted as necessary,
depending upon the rate of setting, to obtain the required
number of penetrations