According to Wookieepedia, The Rise of Skywalker starts:
A year after the battle of Crait
which is roughly when The Last Jedi ended. Said battle occurred in 34 ABY, while the first episode of The Rise of Skywalker, namely the mission to obtain the Sith wayfinder by Kylo Ren and the Knights of Ren, occurred in 35 ABY, i.e one year later.
This conclusion seems to be based upon testimony by John Boyega (the actor playing Finn) in a relevant article by Empire in February 2019:
John Boyega has confirmed the film takes place roughly one year after the events of The Last Jedi.
There is an awful lot of secondary reports on this, but the sole primary source seems to be the above quote by Boyega in Empire, as tweeted here:
As for Boyega himself, when asked in Twitter, replied that he actually doesn't remember: