There are a lot of good answers above, and I'd like to reinforce what others have said: having timestamps around can be good or bad depending on the type of story being told.
I am now going to focus on the idea of timestamps as chapter subtitles. I say timestamps because, depending on the story, it can be hours, days (as in day 1, day 2, ...), dates, months, years, or centuries.
If the story has a 'countdown' feel to it, then it makes sense for every chapter to reinforce it. However, if one chapter is day 1, then all the events in day 1 should be contained in that chapter. If it's not feasible and each day will consistently require more than one chapter, then create the section day 1 and have all the chapters you might want with no more need for timestamped subtitles.
Stories that have a constellation of events happening in August, then a lull in action till December, then another lull and so on, may benefit from a similar approach: start a section titled 'August' then make no more time references.
I find that having every new chapter include a timestamp has two consequences:
1) the timestamp isn't really that important for every single chapter and the reader stops noticing it, so when the timestamp really is important, the reader will gloss over it.
2) the timestamp is important every single time it's given and not having them would diminish the tension (again, the story has a countdown feel to it)
In the specific case of organising lots of POVs within a large plot and its subplots, timestamps would probably be necessary only on occasion so having them at the beginning of every single chapter could be overkill and have the opposite effect as they'd become invivible to the reader.
You could add an in-universe reason for one or two characters to constantly obsess over time and dates, as @Monica Cellio mentions in a comment to the question, but they must make sense within the story and not be artificially created simply to be character-calendars.
Alternatively, have the narrator or characters mention time (seasons, months, celebrations, past events, etc) either at the beginning or the end of the chapter. I feel time references are more likely to be remembered then than in the middle of the chapter. If you do it always at the beginning of every chapter, it becomes unnatural, so it's important to mix it. Moreover, if the events of next chapter follow closely, a time reference at the end of a chapter might mean you need no time reference at all in the entirety of the next chapter.
If you have a chapter end with the general saying 'I have one week to prepare the battle' then the next chapter shows the troops advancing to the battle field, that's all the time reference you'll need. If the chapter after the three-chapter long battle (which required no time references) kicks off with the hero checking his bandaged arm and grumbling that the wound is still far from closing after five days, again, that's all the time reference you'll need.
But if there are spies infiltrating the battle preparation and trying to sabotage the fortress, then you can start each chaper with
day 7: the door must be reinforced and there's not enough material - quick! raid a nearby warehouse!
day 6: the door is still not finished and now the well has been tampered with - find the culprit and fix the problem
day 5: the door is fixed, but there's still no water
day 4: half the soldiers have diarhea from the tampered water - which is nearly purified - but will the doctor fix the soldiers in time?
and so on. In this scenario, avoid very specific time references within the text (narration or dialogue) because that would make the subtitle timestamps unnecessary, but do drop subtle time references. If the section was titled August, do mention the summer heat or the sudden shower so uncharacteristic for the month. It will remind the reader of the timestamp without actually having to repeat it per verbatim. While this isn't that dire for a month, having an actual date as a chapter title and then mentioning it again within the text makes the chapter timestamp completely unnecessary.
Also, avoid long chapter titles. If you want to go with the timestamp, let them be not the subtitle, but the title itself. Then they aren't an extra information in smaller font, but the element around which the chapter was written.