It used to be in the Ranking Criteria (at least I could have sworn it was D:), but now I just realised it's gone (unless my memory is failing me now). It used to be that the minimum time needed before the first object from the start of the song was 2000ms. It might not be in the criteria anymore, but enough time before the first object is still needed, or the player might not be prepared enough to start playing.
What I suggest is that 1500~2000ms is highly recommended to be given before the first object from the start of the song, and if there isn't enough time they should edit the AudioLeadIn in the .osu in Notepad in the editor. I don't know if 1500ms would be adequate time, I would honestly encourage that the baseline mark would be 2000ms because I feel 1500ms isn't enough time, but I have been rebutted against that (and since I just realised it's not a rule anymore, I can't object anything). Not sure if it should be a Rule or a Guideline, but I feel that lead-in is really important and I have no idea why it was taken out of the criteria.
What I suggest is that 1500~2000ms is highly recommended to be given before the first object from the start of the song, and if there isn't enough time they should edit the AudioLeadIn in the .osu in Notepad in the editor. I don't know if 1500ms would be adequate time, I would honestly encourage that the baseline mark would be 2000ms because I feel 1500ms isn't enough time, but I have been rebutted against that (and since I just realised it's not a rule anymore, I can't object anything). Not sure if it should be a Rule or a Guideline, but I feel that lead-in is really important and I have no idea why it was taken out of the criteria.