Is it obligatory to advise someone who has committed several evil deeds to abandon all of them on a single day, or over spaced-out periods?

The ruling on advising a sinner varies according to their situation. If it is highly probable that they will accept the advice, then advising them concerning all their transgressions becomes obligatory, because abstaining from sins is an immediate obligation, as Allah Almighty says: "And hasten to forgiveness from your Lord." If it is highly probable that excessive advice might lead to a detriment, such as their aversion, then one should approach them gradually with advice, as Allah Almighty says: "So remind, if the reminder benefits," meaning as long as the reminder is accepted; otherwise, it would not be commanded.