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The specification¹ says (emphasis is mine):

using IO trigger distance, the high signal to at least 10us.

So, longer than 10 μS is not a problem.

With respect to less than 10 μS, well 5 μS may also work, but it is out-of-spec and therefore not guaranteed to work and so may not always work correctly, or as expected.

From Source 1:

Timing diagram#1

From Source 2:

Timing diagram#2

¹ Sources for downloading HC-SR04 pdf datasheet:

• Source 1
• Source 2

###HC-SR04 Specifications

• Working Voltage: DC 5V
• Working Current: 15mA
• Working Frequency: 40Hz
• Max Range: 4m
• Min Range: 2cm
• Measuring Angle: 15 degree
• Trigger Input Signal: 10μS TTL pulse
• Echo Output Signal Input TTL lever signal and the range in proportion
• Dimension 45 * 20 * 15mm