Praying always with all prayer and supplication in the Spirit, and watching thereunto with all perseverance and supplication for all saints; Ephesians 6:18
D. Sheets shares a thought-provoking idea regarding times for prayer:
"There are two Greek words for "time." One is chronos, which is time in general, the general "time in which everything is done". The other word, kairos, is the strategic or "right time; the opportune point of time at which something should be done".
A window of opportunity would be kairos time.
A well-timed attack in war would be kairos time.
When someone is in danger or about to be attacked by Satan, that is a kairos time.
What time is would be chronos time.
The Bible speaks of well-timed (kairos) temptations (see Luke 4:13; 8:13).
The Scriptures also inform us of strategically-timed persecution (see Acts 12:1; 19:23).
In Ephesians 6:18, the context of which is spiritual warfare, it says we are to "be on the alert...for all the saints" and "pray at all (kairos) times in the Spirit." He is not telling us to pray all the time, which would be chronos, but to pray at all strategic times (kairos).
In other words, we are in a war and if we are alert, He will warn us of the well-timed attacks (kairos) of the enemy so we can create a boundary (pata) of protection by praying. "