The pocket watch is not truly "charged" in the conventional sense, but rather displays an "energy quota."
Once these quotas are exhausted, he doesn't need to deliberately replenish them; they will automatically refresh to the maximum value at midnight.
Its energy mechanism is more akin to a "quota" system.
The role of the Sands of Time, however, is to expand the maximum energy quota of the pocket watch, rather than simply charge it.
This very trait makes the pocket watch the most stable and reliable among all his rare antiques.
"It seems the Sands of Time truly hold the key here..."
Ron thoughtfully caressed the surface of the pocket watch:
"If I can obtain more Sands of Time, increasing the maximum quota to a higher level, the potential of this glory legacy will be even more astounding."
He carefully put away the pocket watch, calmed his mind, and began to keenly feel the various changes after becoming an Advanced Apprentice.