Today I couldn't meditate in the morning, but I was able to meditate later in the day. Why was that?
There could be many reasons. When you tried to meditate in the morning, perhaps you needed or wanted more sleep. You did absolutely the right thing by meditating later. If you had meditated well in the morning, then the time that you spent would have left you totally satisfied. But since you felt you did not meditate properly in the morning, then the best thing was to try again later, which you did.