World's Finest Comics 91
Superman, Batman and Robin were converging on a criminal at Smoky Mountain, but he had prepared a trap for the three heroes, with sleeping gas, cryogenic chambers (and a little Kryptonite). After they went into the chamber, he put them to sleep, then into the chambers, hid the Batmobile as well as the entrance to the cavern....and the heroes weren't found until 1000 years later! Scientists in 2957 were willing to send them home via a time ray, but...it had been stolen! The heroes worked against the criminals of the day, also facing a descendant of Luthor named Rohtul, but it was one of the scientists, Lora, who had taken the time-ray in an attempt to keep Superman in that time. The heroes go back in time, preventing the original criminal from ever triggering his trap....
Adventure Comics 253
Superman is found by Robin, nearly dying, as a Cosmic Clock trophy he had gotten when he was in Smallville had a Kryptonite bomb trap in it. So, Robin gets the idea to travel back in time to when Superboy gets the Cosmic Clock (thanks to Prof. Carter Nichols and his time ray). Superboy stops Robin from destroying the Cosmic Clock as it was a gift to the fair from Superboy. Robin and Superboy handle some very technological crimes during Robin's time in Smallville (eventually finding an older Luthor responsible, as Luthor's origin hadn't happened yet). Then, they do find the clock gift for Superboy....which he throws into orbit, with Robin now feeling secure that he could go back to his own time, having prevented the disaster which would befall Superman.
Paradoxes are fun, no?
They can give you quite a headache....likely making you wish you had gone back in time and NOT decided to read this, and just enjoy the tales as you read them!