At low levels my characters tend to do everything in their power to always be very prepared at all times, unless the character is supposed to be suicidal of course.
If I personally had the ability to make anyone who was wanting to ambush me glow bright pink, but only to me, and it lasted 30 minutes I would
definately waste those 3 seconds anytime I was anywhere. Inside of my locked home I would likely only check around and so long as the door or windows dont open I wouldnt care, but anywhere else that I wasnt in a locked building where no one could get in without setting off alarms? Oh yeah, no getting jumped for me.
So, no, I dont see a reason to not turn it back on every so often.
Given that though, the warlocks in my game who have it (not all of them do) I have told them it lasts for 24 hours for the whole ability.
Unless it came out and said a shorter duration I would go with this.
After all, it only says that you gain the ability to 'see' as the spell, which only tells you how and what they see. The only duration listed is 24 hours, so that must be it for the whole thing.
Going with the opposite however, how long would people have entropic warding last? Do you have the person keep track of all of these seperate durations? I'd rather just go with the 24 hours, as seems to be implied for them all, and leave it at that
(note that stony grasp is different, this power is 'as the spell' in how it works as opposed to 'as the spell' where they talk about the effects)