Jiraiya had a hard time entering Sage Mode, because when he summoned the two Toad Sages, they were brought into the mortal world together with a tremendous amount of Nature Energy.
In contrast to the difficulty of summoning them, once Jiraiya brought the two Sages over, he could enter Sage Mode instantly. At the same time, he could use Sage Art: Twin Life Technique to fuse with the two Sages. This allowed them to continuously absorb Nature Energy for him during battle, making Jiraiya's Sage Mode exceptionally long-lasting.
The defining trait of Senjutsu Chakra was that it did not cause the user's body to become fatigued. On top of that, Jiraiya could continuously produce Senjutsu Chakra, allowing him to maintain an extremely high level of combat strength for a long time.
"Lord Jiraiya's current appearance... what's going on?"
Most of the Konoha Ninja had no idea what had happened. They only knew that Jiraiya seemed to have become incomparably powerful... Apart from Jugo, who was a natural vessel, Jiraiya was the only person in the ninja world who could use Senjutsu at this point. Ordinary ninja simply had no access to information on this level.
Just as both sides were stunned by Jiraiya's "new skin," a flash of lightning suddenly approached him at high speed from the side... It was the Fourth Raikage.
Whether one said he was comparable to the Yellow Flash or merely second to the Yellow Flash, there was no questioning the Fourth Raikage's speed. He closed in at high speed, then attacked without the slightest hesitation:
Lightning Release: Lariat.
Under normal circumstances, most ninja would be instantly killed by this technique. If they somehow weren't killed instantly... just imagine what Sasuke would have felt.
However, Jiraiya was currently in Sage Mode. It gave him superhuman perception