From the MT Hebrew it is clear that God did not create anything ("work"), or even put the finishing touches on anything on the seventh day.
The question arises because of the use of "completed" or "finished" to translate ויכולו instead of "had finished" or "ceased". The English words "completed" or "finished" can indicate the action or work that completes something, but כלה means that the action is already over. The indication comes both from the context and from the other instances of כלה in the MT.
Here are examples of the other instances. First from כִּלָּה , then from כָּלָה. Note the tendency to use pluperfect translations to capture the sense of כלה.
Genesis 18:33 (כִּלָּה)
וַיֵּלֶךְ יְהוָה כַּאֲשֶׁר כִּלָּה לְדַבֵּר אֶל אַבְרָהָם וְאַבְרָהָם שָׁב לִמְקֹמוֹ
And the LORD went his way, as soon as he had left communing with Abraham: and Abraham returned unto his place. (KJV)
Genesis 43:2 (כִּלָּה)
וַיְהִי כַּאֲשֶׁר כִּלּוּ לֶאֱכֹל אֶת הַשֶּׁבֶר אֲשֶׁר הֵבִיאוּ מִמִּצְרָיִם וַיֹּאמֶר אֲלֵיהֶם אֲבִיהֶם שֻׁבוּ שִׁבְרוּ לָנוּ מְעַט אֹכֶל
And it came to pass, when they had eaten up the corn which they had brought out of Egypt, their father said unto them, Go again, buy us a little food. (KJV)
Numbers 16:21 (כִּלָּה) Here in the sense of "finish them off"
הִבָּדְלוּ מִתּוֹךְ הָעֵדָה הַזֹּאת וַאַכַלֶּה אֹתָם כְּרָגַע
Separate yourselves from among this congregation, that I may consume them in a moment.
Now for כָּלָה
Genesis 21:15 (כָּלָה)
וַיִּכְלוּ הַמַּיִם מִן הַחֵמֶת וַתַּשְׁלֵךְ אֶת הַיֶּלֶד תַּחַת אַחַד הַשִּׂיחִם
And the water was spent in the bottle, and she cast the child under one of the shrubs (KJV)
Jer 16:4 (כָּלָה)
מְמוֹתֵי תַחֲלֻאִים יָמֻתוּ לֹא יִסָּפְדוּ וְלֹא יִקָּבֵרוּ לְדֹמֶן עַל פְּנֵי הָאֲדָמָה יִהְיוּ וּבַחֶרֶב וּבָרָעָב יִכְלוּ וְהָיְתָה נִבְלָתָם לְמַאֲכָל לְעוֹף הַשָּׁמַיִם וּלְבֶהֱמַת הָאָרֶץ
They shall die of grievous deaths; they shall not be lamented; neither shall they be buried; but they shall be as dung upon the face of the earth: and they shall be consumed by the sword, and by famine; and their carcases shall be meat for the fowls of heaven, and for the beasts of the earth. (KJV)
I Sam 20:7 (כָּלָה)
אִם כֹּה יֹאמַר טוֹב שָׁלוֹם לְעַבְדֶּךָ וְאִם חָרֹה יֶחֱרֶה לוֹ דַּע כִּי כָלְתָה הָרָעָה מֵעִמּוֹ
If he say thus, It is well; thy servant shall have peace: but if he be very wroth, then be sure that evil is determined by him (KJV)
And now from the context of Genesis 2:1-2 (KJV)
And on the seventh day God ended his work which he had made; and he rested on the seventh day from all his work which he had made.
And God blessed the seventh day, and sanctified it: because that in it he had rested from all his work which God created and made.
We can see that there are no less than three phrases in two verses that indicate that God stopped (as in "done stopped") and rested on the seventh day. This style of repetition in the OT is an indication of emphasis - yes he really was done at the end of the sixth day and rested on the seventh.
- WikiMilon, the Hebrew version of Wiktionary, entry כלה
- Frank Luke's first comment on the OP above