When working with PHP, you may need to set the clock time on a mutable DateTime. This guide explains the operation, shows what its arguments mean, and uses three separate examples to make the result easier to understand.
date_time_set: Updates the time while retaining the calendar date and timezone.
What Is date_time_set in PHP?
Set the clock time on a mutable DateTime. Updates the time while retaining the calendar date and timezone.
Syntax:
date_time_set(DateTime $object, int $hour, int $minute, int $second = 0, int $microsecond = 0): DateTime
Parameters and return value: The signature above identifies the arguments and return type where the API has a single call. For topic guides, follow the sequence of calls in the examples. Always distinguish a returned value from an object or variable modified by reference.
Important: Invalid time components can be normalized. Some local times are ambiguous or missing around daylight-saving changes.
Example 1: Basic Usage
This example introduces the operation with a short and predictable input.
<?php
$date = new DateTime("2026-10-16", new DateTimeZone("UTC"));
date_time_set($date, 9, 30);
echo $date->format("Y-m-d H:i");
Output:
2026-10-16 09:30
The code focuses on the main operation. Updates the time while retaining the calendar date and timezone.
Example 2: Another Case
Now compare a different input, locale, date, or option to see another part of the behavior.
<?php
$date = new DateTime("2026-10-16", new DateTimeZone("UTC"));
date_time_set($date, 14, 45, 30);
echo $date->format("H:i:s");
Output:
14:45:30
What changes? Invalid time components can be normalized. Some local times are ambiguous or missing around daylight-saving changes.
Practical Example: Applying It in an Application
Use the following separate example as a starting point for a small application task. Check any extension or environment requirements below before running it.
<?php
$appointment = new DateTime("2026-10-16", new DateTimeZone("Europe/London"));
$openingHours = ["hour" => 10, "minute" => 15];
date_time_set($appointment, $openingHours["hour"], $openingHours["minute"]);
echo $appointment->format(DATE_ATOM);
Output:
2026-10-16T10:15:00+01:00
The practical example demonstrates how to apply this operation to multiple values, a reusable task, or a validated input. Updates the time while retaining the calendar date and timezone.
Important Behavior and Edge Cases
- Core behavior: Updates the time while retaining the calendar date and timezone.
- Inputs and results: Invalid time components can be normalized. Some local times are ambiguous or missing around daylight-saving changes.
- Alternatives: date_date_set() changes the year, month and day.
Comparison With Related Functions
| Function or Approach | When to Use It |
|---|---|
date_time_set | Set the clock time on a mutable datetime. |
| Related PHP approach | date_date_set() changes the year, month and day. |
Common Beginner Mistakes
| Mistake | Correct Approach |
|---|---|
| Using an incorrect input or option | Invalid time components can be normalized. Some local times are ambiguous or missing around daylight-saving changes. |
| Confusing this API with a related operation | date_date_set() changes the year, month and day. |
| Assuming output is identical across environments | Check return values and required extensions or versions. Use explicit locale, timezone or encoding settings when they affect the result. |
Key Takeaways
- date_time_set helps you set the clock time on a mutable DateTime.
- Updates the time while retaining the calendar date and timezone.
- Invalid time components can be normalized. Some local times are ambiguous or missing around daylight-saving changes.
Use date_time_set when you need to set the clock time on a mutable DateTime. Start with the first example, compare the second, and adapt the practical example to your inputs. Confirm the return value and environment requirements before adding it to production code.