Firstly when looking for quotes to cover the 1440 minutes of the day, I did not have to start from scratch. For the literary clock, the Guardian newspaper did a crowd sourcing effort that managed to cover the more popular minutes of the day. This kickstarted the clock with quotes for around a third of the day, covering especially the popular minutes of the day.
Now for the other 1000 or so minutes. I managed to find the bulk of them using my personal library and the Project Gutenberg collection as described in the following posts. However this left me with slightly more than a handful of times to get. To find some of them I set up a discussion in Goodreads, to enlist other avid readers to help. This definitely provided some crucial and amusing quotes.
Though I was still tantalisingly short of completion. Step forward Google Books. Having worked with up to 50,000 books with the very specific mission of finding times, Google Books is just mind boggling. The big plus of using Google Books is that we can look through 25 million books. The downside is that we have to look through 25 million books. Included in this total are many almanacks and reference books detailing sunrises and sunsets, the tides and other interesting meteorological phenomena to the minute. Alas, not really the literary quotes I was hoping for. Still this definitely helped out with some of the rarer times.
I should also mention another online collection of books, HathiTrust. Looking through their 5 million books, provided some wonderful quotes, including one of the more obscure quotes in the Literary Clock:
He was taken from me, by the inscrutable decree of the Almighty, on the fifth of this month at thirty-three minutes past seven in the morning, and died in peace of an influential attack of the chest — he had been asthmatic of late years, though otherwise in good health, praise God.
The Sin of Joost Avelingh: A Dutch Story by Maarten Maartens
However, as you could imagine inputting these times one by one and reading through all the search results was rather time consuming. Hence why I left this to right at the end, when I was looking for the final minutes to complete the day. The bulk of the quotes would found by instructing a computer to read through books at a much quicker rate than I could.