Canon 665. §1 Religious are to reside in their own religious house and observe the common life; they are not to stay elsewhere except with the permission of the
Superior. For a lengthy absence from the religious house, the major Superior, for a just reason and with the consent of the council, can authorise a member to live outside a house of the institute; such an absence is not to exceed one year, unless it be for reasons of health, studies or an apostolate to be exercised in the name of the institute.

NB Congregation for Institutes of Consecrated life and Societies of Apostolic Life,
Instruction Cor Orans, 1 April 2018:

176. The limitation in the Instruction Verbi Sponsa, n. 17, §2,* has been repealed; for just cause the Major Superior, according to the norm of can. 665, §1 CJC, with the consent of her Council, may authorize the absence from the monastery of a nun with solemn vows for not more than a year, after hearing the diocesan Bishop or the competent religious Ordinary.
[*”It should be noted that the norm of can. 665, §1, on permanence outside the
Institute, does not regard enclosed nuns” Verbi Sponsa, n. 17, §2.]

§2 Members who unlawfully absent themselves from a religious house with the intention of withdrawing from the authority of Superiors, are to be carefully sought out and helped to return and to persevere in their vocation.