when you eat it takes energy to break down and absorb energy. this is the thermal effect of food. so basically energy expended is directly equal to the amount of cals and nutrients in the meals. bigger meal eaten less often will result in a bigger metabolic boost but less often. smaller meals more frequently result in smaller boosts but more frequent. 2500 cal diet eaten in 3 meals or 6 still requires the same amount of energy to use up and absorb, thefor metabolic boost is the same throughout the day no matter how you split up your meals.
metabolic boost can slightly be boosted by eating in the morning by insulin sensitivity. but that is not due to some magical thing about the morning. insulin sensitivity is increased do to liver glycogen depletion as a result of not eating from 8-10 hours (small fast)
also though if you do not eat in the morning and 14-16+ hours past without eating your bady does not go into starvation mode. not for a minimum of 48 hours, and not usually till at least 72-96 hours.up until that 48 hours metabolism is actually increased from an evolutionary perspective. Epinephrine and norepinephrine (adrenaline/noradrenaline) sharpens the mind and makes us want to move around. Desirable traits that encouraged us to seek for food, or for the hunter to kill his prey in primitive times, increasing survival. therefor metabolic rate is increased in short fasts as well