Calvin on When to Pray

John Calvin, Institutes 3.20.50:

But although it has been said above (sec. 7, 27, &c.), that we ought always to raise our minds upwards towards God, and pray without ceasing, yet such is our weakness, which requires to be supported, such our torpor, which requires to be stimulated, that it is requisite for us to appoint special hours for this exercise, hours which are not to pass away without prayer, and during which the whole affections of our minds are to be completely occupied; namely, when we rise in the morning, before we commence our daily work, when we sit down to food, when by the blessing of God we have taken it, and when we retire to rest. This, however, must not be a superstitious observance of hours, by which, as it were, performing a task to God, we think we are discharged as to other hours; it should rather be considered as a discipline by which our weakness is exercised, and ever and anon stimulated. In particular, it must be our anxious care, whenever we are ourselves pressed, or see others pressed by any strait, instantly to have recourse to him not only with quickened pace, but with quickened minds; and again, we must not in any prosperity of ourselves or others omit to testify our recognition of his hand by praise and thanksgiving.