I believe you're correct. From the spec, however, it doesn't mention this specific time. It does mention other message scheduling.
From page 2-8 of COMDTINST M16577.1 APR 21 1993
I. MESSAGE SCHEDULING
1. In general, the data stream will consist mainly of message types
3, 7, & 9 as the broadcast of message types 5 and 16 will be
rather infrequent. Due to the advent of continuous tracking
receivers the Type 2 Message is no longer required and its use
would only serve to increase the latency of the broadcast. For
each new Issue of Data (IOD) their will be a 90 second delay
before the broadcast pseudorange corrections are computed with the
new IOD. Ninety seconds should be more than adequate for a
continuously tracking DGPS receiver, as it will be able to
instantaneously read the navigation messages as they are broadcast
from each satellite. Sequencing Receivers are not to be used for
navigational purposes within the USCG Differential GPS Navigation
Service. Any shading of a satellite at IOD, such as passing under
a bridge, are compensated for by the ninety second delay. This
method of handling a new IOD requires the user equipment suite to
store both the new and the old IOD for the subject period. No
ancillary messages will be broadcast within 90 seconds of each
other under any circumstances.
a. Type 3 Message: Type 3 Messages will be broadcast at fifteen
and forty-five minutes past the hour.
b. Type 5 Message: If an unhealthy satellite is deemed usable
for DGPS, a Type 5 Message will be broadcast at five minutes
past the hour and every fifteen minutes thereafter. If an
unhealthy satellite which was deemed usable is later deemed
unusable the reference station will no longer broadcast
corrections for the subject satellite.
c. Type 7 Message: A routine Type 7 Message will be broadcast at
ten minute intervals beginning at seven minutes past the hour.
Type 7 Messages will be updated and broadcast within two
minutes if the status of a beacon changes for which they
contain information. This will aid the user equipment suite in
its choice of the proper beacon.
d. Type 9 Message: Corrections will be broadcast only for
satellites at an elevation angle of 7.5 degrees or higher
through use of the Type 9 Message. The official GPS coverage
which is provided is based on elevation angles of ten degrees
or higher. Satellites at elevation angles lower than 7.5
degrees are adversely effected by spatial decorrelation,
multipath, and minimal processing time between acquisition and
actual use. The level of 7.5 degrees is identical to that
recommended by RTCA Special Committee 159. Corrections for a
maximum of nine satellites will be broadcast. If more than
nine satellites are above a 7.5 degree elevation angle, a
situation which occurs less than one percent of the time, then
corrections are broadcast for the nine satellites with the
highest elevation angles. If the choice is between two
satellites with elevation angles which are greater than 7.5
degrees, but within two degrees, the descending satellite is
chosen. Positioning users of the system who are interested in
achieving the highest accuracy level possible should use a
higher mask angle in order to avoid the higher atmospheric
effects associated with low elevation satellites. When a
reference station drops a satellite it will broadcast an
indicatiouser equipment suite per 4.E.1 to stop applying
corrections for that satellite to its navigation solution.
e. Type 16 Message: This message type will be broadcast as
deemed necessary but within strict limits. Type 16 Messages
will not be broadcast for a period of at least ninety seconds
preceding or following a Type 3, 5, or 7 Message and the
interval between successive Type 16 Messages will be no less
than three minutes.
Topic: DGPS Logs Mar 12, 2017 UTC 1328 - Mar 12, 2017 UTC 2328 (AFE822x) (Read 865 times)