In the battle of Vegito vs merged Zamasu we saw Vegito fused lasted very little because Vegito was so powerful that the power of the earrings were consumed to keep Vegito together. If Goku and Vegeta would use the earrings in the tournament of power to fuse and become Vegito, and after a very short time they defused again, could those potara earrings be used to fuse other warriors, like for example 17 and 18?
This image is right after Goku and Vegeta defuse vs Merged Zamasu. We see the Potara earring on Vegeta's right ear and Goku obviously has it on his left ear. Also, even during the fight between Vegito and Buuhan (Super Buu with ultimate Gohan absorbed), there is a scene where Goku and Vegeta defuse inside him and Vegeta breaks the Potara earring. So Goku and Vegeta could give the Potara earrings to say someone like Android 17 and 18 right after and have them fuse if they wanted to.
It has never been mentioned that the Potara earrings require a time limit to be used, like the fusion dance. If the time limit were to apply, it would be on the warriors themselves and not the Potara earrings as the earrings themselves don't provide any additional energy to the warriors and it only acts as some form of a multiplier which fuses the energy between the two warriors.
Could they refuse after the fusion ends is a question you should be asking akria toriyama not the internet since it wasn't explained i am gonna go with yes they could refuse however they were so exausted that they couldn't move so refusing with the potara to become vegetto would not have been any good the only way that they could have killed merged zamasu was if goku had tapped into autonomous ultra instinct or if vegetto had used a kaioken times twenty while a super saiyan blue and obliterated zamasu if they had refused while exausted most likely vegetto would be pushed to the limit and tap into autonomous ultra instinct where he would have to kill zamasu so nothing remains or else he would have done that universe bullshit where even a fully powered mastered autonomous ultra instinct vegetto could not destroy infinite zamasu without taking himself and the universe along with him