Yes, this is one of many things believers are divided over, at least those who choose to divide over it. Though I believe that earth was probably created about 6000 or so years so, there are old earth creationists I can fellowship and some I probably couldn't.
In this thread I have not mentioned anything about 24 hour days, though that does correspond with what I believe about the 7 days in Genesis 1-2, however ill-informed it may be.
However, make the days what you will -- 6 hours, 12 hours, 24 hours, 1 year, 100 years,1000 years, 1 million years, 1 billion years -- Genesis 1 still says God created the sun, moon and stars on the fourth day. This would be the day after what he created on the third day (grass, herb, fruit tree) , and the day before what he created on the fifth day (fish, fowl, etc.).