Of course, he didn't use the item right away.
The reason was simple: the cooldown period for this item was too long, a full seven days. After lifting this absolute seal, if other restrictive effects were thrown at him, it would be somewhat troublesome.
Although it wouldn't pose any danger to him, it would still be quite a hassle.
As for danger...
During the last global event, he had spent tens of millions of Blood Battle Points to purchase dozens of Rule Items suitable for dealing with different predicaments, plus a series of Rule-defensive tools such as the Rabbit Badge. To put it bluntly, even if he were to face the current predicament...
Even if he were thrown into the universe and exposed to the vacuum of space, bombarded by countless messy cosmic rays from all directions, he could still survive for a few minutes.
And these few minutes would be enough for him to use the "Legacy of the River of Time" to return to a day earlier, and then change the outcome of today.