Question:  "Does Genesis chapter 1 literally mean 24-hour days?” 

Answer:  The English word "day" can mean more than one thing.

It can refer to the 24-hour period of time that it takes for the earth to rotate

on it's axis (i.e. "there are 24-hours in a day"). It can refer to the period of

daylight between dawn and dusk (i.e. "it gets pretty hot during the day but it cools down

a bit at night"). And it can refer to a unspecified period of time

(i.e. "back in my Grandfather's day..."). Likewise, the Hebrew word "yom"

(which translates into the English "day") can mean more than one thing.

 It is used to refer to a 24-hour period in Genesis 7:11. It is used to refer to the

period of daylight between dawn and dusk in Genesis 1:16. And it is used to

refer to an unspecified period of time in Genesis 2:4. So what does it mean in

Genesis 1:5-2:2 when it's used in conjunction with ordinal numbers (i.e. " the first day,

" & " the second day,"  & "the third day," & " the forth day," " the fifth day,"

" the sixth day," and "the seventh day")? Are these 24-hour periods or

something else? Could "yom" as it is used here

mean an unspecified period of time? How can we tell?

Yes we can determine how "yom" should be interpreted in Genesis 1:5-2:2 simply by

examining the context in which we find the word used and then comparing it's context with how

we see its usage elsewhere throughout scripture. By doing this we let Scripture interpret itself.

Ken Ham of Answers in Genesis wrote a good article on this. It's published at - http://www.answersingenesis.org/cec/study_guides/answersSG2.pdf. 

Mr. Ham writes, "The Hebrew word

for day (yom) is used 2301 times in the Old Testament. Outside of Genesis 1:

Yom + ordinal number (used 410 times) always indicates an ordinary day

[i.e. a 24-hour period]. The words ‘evening’ and ‘morning’ together (38 times)

always indicate an ordinary day. Yom + ‘evening’ or ‘morning’ (23 times each)

always indicates an ordinary day. Yom + ‘night’ (52 times) always indicates

an ordinary day."

Now let’s look at the context in which we find the word "yom" used in Genesis 1:5-2:2...

Day 1 -

"And God called the light 'day' [yom] and the

darkness he called 'night.' So the EVENING and the MORNING were the

FIRST DAY [yom]." (Genesis 1:5)

Day 2 -

"So God called the firmament 'Heaven.' So the EVENING and the

MORNING were the SECOND DAY [yom]." (Genesis 1:8)

Day 3 -

"So the EVENING and the MORNING were the THIRD DAY [yom]." (Genesis 1:13)

Day 4 -

"So the EVENING and the MORNING were the FOURTH DAY [yom]." (Genesis 1:19)

Day 5 -

"So the EVENING and the MORNING were the FIFTH DAY [yom]." (Genesis 1:23)

Day 6 -

"Then God saw everything that He had made, and indeed it was very good.

So the EVENING and the

MORNING were the SIXTH DAY [yom]." (Genesis 1:31)

Day 7 -

"Thus the heavens and the earth, and all the host of them, were finished.

And on the SEVENTH DAY [yom] God ended His work which He had done,

and He rested on the SEVENTH DAY [yom] from all His

work which He had done." (Genesis 2:1-2)

It is quite clear by the context that the Author of Genesis chapter 1 meant 24-hour periods.

This was the standard interpretation up until the 1800s when a paradigm shift occurred

within the scientific community and the Earth's sedimentary strata layers were reinterpreted.

Whereas previously the rock layers were interpreted as evidence for Noah's flood,

Noah's flood was thrown out by the scientific community and the rock layers were

reinterpreted as evidence for an excessively old earth. Some well meaning but terribly

mistaken Christians then sought to reconcile this new anti-Flood, ant-Bible interpretation

with the Genesis 1 account by reinterpreting "yom" as meaning vast unspecified periods of time.

This was a mistake.

The truth is, the evidences in favor of Noah's flood and a young earth far

outnumber those in favor of an old earth and many of the old earth

interpretations are known to rely upon faulty assumptions.

Unfortunately the scientific community is entrenched on the matter

and apparently they refuse to change their minds despite the

weight of evidence contrary to their currently accepted paradigm.

But please don't let their stubborn refusal influence how you read your Bible!

According to Exodus 20:9-11, God used six literal days to create the world

in order to serve as a model for man's work week. Work six days, rest one.

Rest assured, God could have created everything in an instant if He wanted to. But

apparently He had us in mind even before He made us (on the sixth day) and wanted

to provide an example for us to follow