In Flash #125 (October 1961), Wally West, aka Kid Flash, goes to visit his aunt and ends up spending time with Barry Allen, aka the Flash. We learn that since time travel has become an important part of being a speedster, that Barry has invented a “cosmic treadmill”.
Barry explains that the treadmill helps a speedster reach the right “vibration frequency” for time travel and then it’s up to the speedster to maintain that vibration in the new time period. If the speedster lets the vibration go, they automatically return to their own time period.
And away those two speedsters go, one into the past and one into the future for some adventures.
Incidentally, October 1961 seems to be the month where both DC (National) and Marvel decided to up the cost of their comics from 10 cents to a whopping 12 cents. Inflation!