California Code, Health and Safety Code - HSC § 41703

If a district board adopts a rule or regulation of emission standards to take effect as of a future date, the rule or regulation shall also require any person who owns or operates a source of air contaminants whose emissions exceed such standards to submit to the hearing board, for a public hearing, after notice pursuant to Section 40826, a schedule of increments of progress by which the source emissions will be brought into compliance by the time such standards take effect.

If the rule or regulation itself includes a schedule of increments of progress, the person shall apply for a modification in accordance with Section 42357 in the event he cannot comply with the schedule in the rule or regulation, except that an application for a change in the final compliance date shall be subject to the requirements for a variance, as provided in Section 42352.