Area under the curve in a drug concentration curve
This definition of AUC is non-standard.
The usual definition does not involve the MIC or 24h: it is the area (~ integral) of the plasma concentration curve as a function of time, from first administration time $t_0$ time to infinity. (You will sometimes see it subscripted as $\mathrm{AUC}_{0 \to \infty}$)
In the case of so-called time dependant antimicrobials (beta-lactams, macrolides, vancomycin), the bacteria are inhibited from replicating as long as the concentration stays above the MIC (minimal inhibitory concentration). Often a second threshold, the MBC (minimal bactericidal concentration) is defined corresponding to the required concentration to kill rather than just inhibit replication.
As you stated, the second strategy has indeed a longer duration above MIC. It is more effective from a purely kinetic standpoint. Whether than translate to clinically relevant effects depends on the antibiotics, the bacteria and the tissue under consideration.
A second point is whether a higher AUC is beneficial if the time spent above MIC or MBC is the same (nb: not the case here). However this also depends on factors beyond just pharmacokinetics.
As an aside, some antimicrobials like the aminoglycosides display a &quot;concentration dependant&quot; effect where the peak drug concentration determines the effect, dictating different dosing schedules.