How long you fast, the kind of fast you undertake, and how you adjust your work schedule depends mostly on your occupation. Persons with office jobs, pastors, or homemakers may find it easier to continue their duties and fast for longer periods of time. In fact, on the basis of my personal experience, worldwide travels and the many letters, which I have received, I am confident that many, many thousands of pastors and lay men and women have already completed a 40-day fast!
Though there are many who engage in strenuous physical labor and have enjoyed their extended fast, if you are so engaged, you may wish to fast only one or more days of the week, limiting yourselves to partial fasting if you are so engaged. Or you may look to weekends as the prime time to abstain from food. Remember, too, fasting during major holidays is not always a good idea. Families may be inconvenienced, and temptations to eat can be overwhelming.
Reasons for schedule adjustments, especially during an extended fast, are two-fold...
The first is physical. Throughout your fast, you may feel somewhat weaker than normal. During the first few days, you may feel tired and irritable. Lightening your workload and cutting down on strenuous exercise would be a very good idea to maintain your health and your morale.
The second reason is spiritual. Fasting is not just denying yourself food. It is exchanging the needs of the physical body for those of the spiritual. Long times of prayer and reading God's Word will be very essential if you are to enter into a more intimate communion with God to maintain your fast to its completion. While fasting, if you dissipate your energy on numerous errands or busy-work to the neglect of spending special time with God, you will starve both physically and spiritually. You will find yourself becoming discouraged and frustrated with your fast instead of being benefited and uplifted and blessed. I don't want that to happen to you.
The more time you spend with God in fellowship, worship, and adoration of Him, and the more you read and meditate upon His Word, the greater your effectiveness will be in prayer and the more meaningful your fast will be. So I encourage you to arrange your schedule accordingly!