The ability to travel through time is part of the "weird science" of the Tackleford universe, and has happened (both intentionally and accidentally) on several occasions.
Tim Jones invented a teapot time machine, which was stolen by Amy and Shelley and used by that pair to travel into the 1800s and have a number of adventures including introducing Beatles songs to 19th-century Britain, but this was cut short by Tim using another similar time machine (he was revealed to have a whole cabinet full of them) to go back to just before they stole the machine and stop them, thus causing their whole adventure never to have happened.
A time warp sent waves of ninjas from medieval Japan into Fallon Young's house, but their role was never more than that of a minor nuisance, though it did prompt Shelley to move out of Tackleford to a more peaceful place in the country.
Another time warp was opened by an explosion in Griswald's Grammar School in July 1960, leading to a portal from the day it opened into the 2010s, where the day of its opening was reachable as an infinitely-looped day, in which most attempts to change history failed, but occasionally something somebody did while in the past did have repercussions as seen in "The Case of the Forked Road".
A one-off strip, probably not part of the regular Tackleford continuity, featured the band Summer Camp going back in time with a nuclear powered time travel device to gain musical ideas from 1990; it's not like any songs from that lost era can be found in places like YouTube, Spotify, or iTunes.
The "Destroy History" strip chronicles Shelley's adventures in the Ministry of History, a governmental body devoted to repairing the world's timeline. The existence of this agency may be related to the fact that the government has attempted to regulate time travel via the 2011 TARDIS Act, which Tim was arrested for violating when the authorities became aware of his possession of the Teapot That Reverses Time.