54-2. It is both a privilege and a duty, plainly enjoined in the Bible, to make regular, weekly, systematic and proportionate offerings for the support of religion and for the propagation of the Gospel in our own, and foreign lands, and for the relief of the poor. This should be done as an exercise of grace and an act of worship, and at such time during the service as may be deemed expedient by the Session.

DIGEST: The current text remains essentially unchanged from that of PCUS 1894. For some reason, the final phrase "by the Session", which had been present in the original 1894 text, was deleted with the 1929 PCUS revision. As the PCA's Proposed BCO was based upon the 1933 PCUS text, that deletion was carried forward into the approved 1973 text, with the deleted phrase returned to the paragraph in 1975. See M3GA, 3-70, p. 83.
It should also be noted that from 1894 until 1929, the PCUS had its edition of this paragraph located in chapter VI, on the preaching of the Word The text was removed to a separate chapter on offerings beginning with the 1929 PCUS revision of the Directory for Worship.

BACKGROUND AND COMPARISON :
PCA 1975, DfW 7-2 [M3GA, 3-70, p. 83]
It is both a privilege and a duty, plainly enjoined in the Bible, to make regular, weekly, systematic and proportionate offerings for the support of religion and for the propagation of the gospel in our own and foreign lands, and for the relief of the poor. This should be done as an exercise of grace and an act of worship, and at such time during the service as may be deemed expedient by the Session.

1. PCA 1973, Adopted text, DfW 7-2 [M1GA, Appendix, p. 157]
2. Continuing Presbyterian Church 1973, Proposed text, 7-2, p. 66
3. PCUS 1933, VII, §329
4. PCUS 1929, VII, §329
It is both a privilege and a duty, plainly enjoined in the Bible, to make regular, weekly, systematic and proportionate offerings for the support of religion and for the propagation of the gospel in our own and foreign lands, and for the relief of the poor. This should be done as an exercise of grace and an act of worship, and at such time during the service as may be deemed expedient.

1. PCUS 1925, VI-6. §327
2. PCUS 1894, VI-6
It is both a privilege and a duty plainly enjoined in Scripture to make regular, systematic, and liberal offerings for the support of religion, and for the propagation of the gospel in our own and in foreign lands, as well as for the relief of the poor. This should be done as an exercise of grace and an act of worship, and at such time during the service as may be deemed expedient by the Session.

COMMENTARY:
Morton H. Smith, Commentary on the Book of Church Order, 6th edition, 2007, p. 425-426.
This paragraph is obviously based on I Cor. 16:1-2 (cited above [in the comments on BCO 54-1]). We are reminded that it is both a privilege and duty to worship God through our weekly giving. If we give our offerings on a monthly basis, we miss out on the weekly acts of worship. Note that the Session may call for offerings at other times than the stated weekly worship services.