An Offer in Compromise can be submitted at any time as long as it is not solely used as a tactic to slow down the collection process. This means that a taxpayer can submit an Offer in Compromise during the examination process, at appeals, after a case is in Tax Court, and in another other stage of the collection process. The earlier the better though, when you submit an Offer in Compromise collection activity is forced to cease until after the offer has been either accepted or rejected.
It is important to review your financial position as closely as possible before submitting an Offer in Compromise. The offer will suspend the statute of limitations in regard to the liability and therefore you should weigh the ability to having your offer accepted by the IRS.