I have the same problem . Time changes at 10 sec. per minute thats 6 minutes per minute. after 50 miles it starts correct time. I wonder is there a battery that keeps time when bike is off?
I no longer have my 1500 but I have helped others with this problem. The reason your time shifts until the bike warms up is that Honda borked up this part of their design. They have a clock that gets set with the switch on the dash but they left the input to the clock chip too high of impedance for all conditions that a bike will experience in the real world.
Two things work against that in the environment (besides electrical noise).
2. contaminants between connections.
The two together can overcome the high impedence and cause the clock chip to think the adjustment switch is engaging. Even if just intermittently.
This is why your clock is doing screwy stuff until the bike warms up and drives the humidity away at the connector, despite any impurities.
This is also why cleaning things often helps but the best thing to do is to overcome the high impedance of the clock inputs where the time setting wires enter the clock module.
To do this I suggest adding a 10K ohm resistor (any wattage) to both inputs and the other end of the resistors both go to the + voltage driving the clock. This makes the inputs to the clock impedance 10k rather than higher. This overcomes both 1 and 2 above
The switches themselves normally switch to ground when adjustments are being made and since they are low impedance devices, they easil override the 10k pull up resistors. You can also use 4.7k or even less but 10k should do the job and if you get too low, you will be putting too much current thru the resistors when making time adjustments.
This problem and others like it are most often seen in high humidity areas like Florida and England. It is also seen in bikes stored over the winter in unprotected cold areas until the bike gets run and warmed up for the season.
As I said, I no longer have my GL but as I recall this is the best way to overcome the environmental optimism of the Honda engineers.