Now that the weather is getting wetter and colder, I'm experiencing more of those moments. It's OK during the week - I have to get to work, and the later I leave, the worse the traffic will be. Is there really much difference between leaving at 0600 when it's 12 degrees and raining or at 0700 when it's 13 degrees and raining and the roads are full of half asleep drivers who are more dangerous than a Nigerian with your bank account details.
The weekends are something altogether different. I don't have to do anything, but I like to get up early and get some exercise and preferably a bit of social interaction with some other cyclists.
The clearest indicator of whether I will ride or not is my guts. I have some sort of subconscious connection between the lizard component of my brain and my bowels. If the primeval part of my brain knows I am going to ride, then the bowels start moving and it's game over - I have to get up, crap and then go do a few miles.
I think this is because I went for an early morning swim many years ago, and found that as I was walking towards the beach just before sunrise, I had an absolutely overwhelming need to do an enormous crap. It's a good thing the public toilets at North Bondi were open at that hour - otherwise, I would have crapped on the grass out of sheer necessity. There was no holding it back.
Since then, my guts have never let me leave the house for any form of exercise without voiding themselves first. It doesn't matter what I'm doing - swimming, skiing, running, cycling or just going for a long stroll - the guts are taking no chances. They're never getting caught short again.
So for me, I don't have to stuff around trying to decide whether to ride or not. If the guts say "go", I go. And frankly, they usually make better decisions than my brain.