Keeping in mind that all Reformed confessions were written in their own context and for their own purposes, we see that the "differences" are not in substance, but in emphasis. The men's fellowship of my parish is going through
Reformed Confessions Harmonized and I posted a few words about this
here.
When one looks at Heidelberg Catechism, Q&A 103 and compares it to Westminster Larger Catechism, Q&A 115–121, this is shown.
The emphasis in the HC is on attendance at public worship as well as the eschatological aspect of the Sabbath day.
The emphasis in the WLC is on the day of the Sabbath (116) and the duty of resting that day (117–121).
Yet, the HC also speaks of "the day of rest," albeit in passing, while the WLC also mentions public worship, especially in Q&A 117.
Finally, any doubts about whether the so-called "Continental" view of the Sabbath is in any way less strict than the English view are laid to rest by the Synod of Dort's doctrinal deliverance (things the Synod of the churches declares that are binding on all the churches) of its 164th session on May 17, 1619:
1. There is in the fourth commandment of the divine law a ceremonial and a moral element.
2. The ceremonial element is the rest of the seventh day after creation, and the strict observance of that day imposed especially on the Jewish people.
3. The moral element consists in the fact that a certain definite day is set aside for worship and so much rest as is needful for worship and hallowed meditation.
4. The Sabbath of the Jews having been abolished, the day of the Lord must be solemnly hallowed by Christians.
5. Since the times of the apostles this day has always been observed by the old catholic church.
6. This day must be so consecrated to worship that on that day we rest from all servile works, except those which charity and present necessity require; and also from all such recreations as interfere with worship. (Cited in Howard B. Spaan,
Christian Reformed Church Government [Grand Rapids, MI: Kregel Publications, 1968], 208.)