Guides / How to time songs
All this is best done before timing, as any audio edits, including re-encoding, will change the timing. ... This is best explained using a metronome. If you wish, you can read the article about Time Signature or take a peek at Alace's thread. ... Then, using the same technique, shift it back to the very first beat of the song, because it affects the pulse of osu! ... This is vital, because you'll have to do lots of test plays, and mistimed hits will make it frustrating to the player.
What do I do? ... (F3) That is, use the osu!metronome and try to catch a change, then test it like a normal single offset.