What is the timerange of a short fast religiously?

The scriptures described people fasting for forty days on end. God does not expect that from us. A fast that is acceptable to the Lord is going without food or water for 24 hours, or basically skipping two meals. Now just fasting won't do you any good. Fasting with prayer, having faith in the Lord Jesus Christ, and praying that HIS WILL be done (not yours) will be acceptable to our Father in Heaven. Another good idea would be to consider how much two meals would cost you at a restaurant. $20? Spend your day in fasting and prayer, and then donate that $20, or whatever amount you can, to the poor. Your faith in God, your obedience to His will, and your willingness to sacrifice will tell God that you are serious in seeking His help, and He will answer you in quiet, peaceful ways.