In Re the Marriage of: Diana Christine Durkee, petitioner, Appellant, vs. Robert Lynn Durkee, Respondent.

may not be cited except as provided by

Minn. Stat § 480 A. 08, subd. 3 (1996).

 STATE OF MINNESOTA

 IN COURT OF APPEALS

 C2-98-1797

David Nels Nyrud, petitioner,

Appellant,

vs.

Commissioner of Public Safety,

Respondent.

 Filed April 13, 1999

 Affirmed

 Lansing, Judge

Pine County District Court

File No. 58-CX-98-347

Mike Hatch, Attorney General, Michael R. Pahl, Assistant Attorney General, 525 Park Street, Suite 200, St. Paul, MN 55103-2040 (for respondent)

William Starr, Charles A. Beckjord, 208 Grain Exchange Building, 400 South Fourth Street, Minneapolis, MN 55415 (for appellant)

Considered and decided by Lansing, Presiding Judge, Schumacher, Judge, and Willis, Judge.

 U N P U B L I S H E D O P I N I O N

 LANSING, Judge

David Nyrud appeals the Commissioner of Public Safety's revocation of the school bus endorsement to his driver's license. Although the state failed to act on the revocation until after the ten-day statutory period expired, we conclude that the ten-day requirement is directory rather than mandatory, and we affirm.

 FACTS

The Commissioner of Public Safety revoked David Nyrud's driver's license under the implied consent law for driving with an alcohol concentration in excess of .20. The driving incident occurred on January 5, 1998, and the license was revoked on February 12, 1998. On March 2, 1998, 18 days after the license revocation, the Commissioner of Public Safety mailed Nyrud a notice that it was also revoking his school bus endorsement. The revocation of Nyrud's endorsement was effective March 15, 1998.

Nyrud challenged the revocation as untimely under Minn. Stat. § 171.3215, subd. 2 (1996), which requires the Commissioner of Public Safety, within ten days of receiving notice of revocation of a driver's license of a school bus driver under Minn. Stat. § 169.123 (1996), to revoke the driver's school bus endorsement. The district court sustained the commissioner's revocation of Nyrud's school bus endorsement. Nyrud challenges the court's holding.

 D E C I S I O N

The commissioner revoked Nyrud's school bus endorsement under Minn. Stat. § 171.3215, subd. 2, which provides:

[W]ithin ten days of revoking a school bus driver's license under section 169.123, the commissioner shall cancel the school bus driver's endorsement on the offender's driver's license or the nonresident's privilege to operate a school bus in Minnesota for five years.

Statutory interpretation is question of law, which we review de novo. State by Beaulieu v. RSJ, Inc., 552 N.W.2d 695, 701 (Minn. 1996). Nyrud contends the term "shall" is mandatory and that the commissioner's failure to act within ten days removes the commissioner's authority to revoke a school bus endorsement.

Although the term "shall" suggests a mandatory act, it may also simply direct action. Wenger v. Wenger, 200 Minn. 436, 440, 274 N.W. 517, 519 (1937). If the action is incidental or subsidiary to the main purpose of the statute, the statute is not designed to protect third persons, and the statute does not state the consequences for failure to comply, then the statute should be construed as directory rather than mandatory. Id. Moreover, "statutory provisions defining the time and mode in which public officers shall discharge their duties, and which are obviously designed merely to secure order, uniformity, system, and dispatch in public business, are generally deemed directory." Id. at 438, 274 N.W. at 518, quoted by Heller v. Wolner, 269 N.W.2d 31, 33 (Minn. 1978).

The main purpose of Minn. Stat. § 171.3215 is to prevent people who have driven under the influence or declined an intoxication test from operating school buses. See Minn. Stat. § 171.3215 (1996 & Supp. 1997). The requirement that the endorsement be canceled is designed to protect third persons, but constricting action beyond a ten-day period is not. Instead, the ten-day period provides a standard for the commissioner to establish a uniform system for the department's actions. Furthermore, the statute does not contain consequences for failure to comply with the time limit. Thus, the subdivision's use of "shall" contains all of Wenger's indicia of a directory phrase.

We reject Nyrud's argument that Thompson v. Commissioner of Public Safety, would support a different result. 567 N.W.2d 280 (Minn. App. 1997), review denied (Minn. Sept. 25, 1997). First, in Thompson, the court interpreted the statute's use of "and" rather than "shall." Id. at 283. Second, the court interpreted "and" to mean "or" to construe the statute according to the legislature's obvious intent. Id. Our holding parallels the reasoning in Thompson that a term should not be interpreted contrary to the intention of the legislature. See Minn. Stat. § 645.16 (1996) (court must interpret statute to effect legislature's intent).

Nyrud, relying on estoppel principles, also asserts that unless the department is limited to the ten-day period, a person may be detrimentally affected by the department's failure to act. Although equity may require a revocation be rescinded in certain situations, see, e.g., Greenlee v. State, 330 N.W.2d 713, 715 (Minn. 1983), this is not such a case. Nyrud has shown no reliance on the department's failure to act within the ten-day period, and the department's further delay of eight days is not arbitrary or capricious. The district court properly sustained the commissioner's revocation of Nyrud's school bus endorsement.

  Affirmed.