I was told in this answer to another question: "The Rambam did not take the '6 days' of Bereishis literally, as well as other details." The answer linked to Moreh Nevuchim (link) but I couldn't find on that page where he really said that it wasn't in six days. In fact, it was my understanding that Rambam and others did take Masay Bereishis as happeneing in six 24 hour days, although I don't know a specific source. What does Rambam say on the issue in Moreh Nevuchim and elsewhere?
In a broad sense the answer is no, the Rambam did not take the six days literally: “First, the account given in Scripture of the Creation is not, as is generally believed, intended to be in all its parts literal.” ( Guide for the Perplexed 2:29, Friedlander page 211).
Precisely what he did view is complicated by the fact that he believed the topic was esoteric and under normal circumstances prohibited to be committed to writing.
The Rambam's view, insofar as I can tell, did not necessarily preclude a literal six days or an interpretation that was "literal" in a very broad sense. His interpretation, as I can tell, seems to predicated on a number of key words not being understood as they would be taken on first impression but instead given a philosophical definition. In a sense I think you could make the case that the Rambam did not reject the plain meaning but what he viewed as an over simplistic reading.
Along these lines the Rambam defends the plain meaning against Aristotelian philosophy (2:17) prior to giving his own interpretation. And remember the Rambam explained that, “a mere argument in favour of a certain theory is not sufficient reason for rejecting the literal meaning of a Biblical text.” (Guide for the Perplexed II:25, Friedlander).
The Rambam, in various places throughout his Mishneh Torah book, which is a book of Halacha's, clearly takes the creation account literally. Just one of the many examples of this came to mind right at the introduction (towards to end):
ועוד חיברו הלכות פסוקות בענין איסור והיתר וחיוב ופטור בדברים שהשעה צריכה להם כדי שיהיו קרובים למדע מי שאינו יכול לירד לעומקה של גמרא. וזו היא מלאכת ה' שעשו בה כל גאוני ישראל מיום שחוברה הגמרא ועד זמן זה שהיא שנה שמינית אחר מאה ואלף לחרבן הבית, והיא שנת ארבעת אלפים ותשע מאות ושלשים ושבע לבריאת עולם:
Also, [the Geonim] composed [texts recording] the decisions of Torah law regarding what is permitted and what is forbidden, when one is liable and when one is free of liability, with regard to subjects that were necessary at the time, so that they would be accessible to the grasp of a person who could not comprehend the depths of the Talmud.34 This is the work of God, which was performed by all the Geonim of Israel from the completion of the Talmud until the present date, 1108 years after the destruction of the Temple, 4937 years after the creation of the world.35
There are other sources in Kiddush Hachodesh where the Rambam mentions the date of him writing his book since creation, as well as another law (DON'T remember the exact source) where he says that one must date a document from the time of creation (I would really like to find that source I KNOW it's in Mishneh Torah somewhere but if someone can find it that would be great), and if the 6 days weren't literal, but it was really millions of years (Chas Veshalom), how can the Rambam state as a halacha that one should sign the date from the time of creation?
In Moreh Nevuchin doesn't at all say the 6 days aren't literal, only that some details aren't meant to be taken as face value, like Hashem physically speaking or other examples of Hashem being personified... but it in no way implies at all that the actual time of creation wasn't literal, Chas VeShalom.