IP = Ingress Protection
5 = Dust protected
Desc - Ingress of dust is not entirely prevented, but it must not enter in sufficient quantity to interfere with the satisfactory operation of the equipment; complete protection against contact
7 = Immersion up to 1 m
Ingress of water in harmful quantity shall not be possible when the enclosure is immersed in water under defined conditions of pressure and time (up to 1 m of submersion).
Test duration: 30 minutes
Immersion at depth of at least 1 m measured at bottom of device, and at least 15 cm measured at top of device
The reason why it's not 8 because for you to be able to get IP58
8 = Immersion beyond 1 m
Desc: The equipment is suitable for continuous immersion in water under conditions which shall be specified by the manufacturer. Normally, this will mean that the equipment is hermetically sealed. However, with certain types of equipment, it can mean that water can enter but only in such a manner that it produces no harmful effects.
Test duration: continuous immersion in water
Depth specified by manufacturer
and to get the IP6
6 = Dust tight
Desc: No ingress of dust; complete protection against contact
The highest level is IP68 which requires a dust tight and is capable of staying underwater for an unlimited time. Like submarines.
But this isn't dust tight because of the open ports. And also this can't emerge underwater for an unlimited time because the body isn't airtight and moisture can develop inside the case if submerged longer.
So.......... It is only stated to last 30minutes underwater because that's the criteria level of IP rules is not very specific enough.
So sony only have 2 choices for this... Either go with the rule to state the device that it can be submerged 1meter for 30 minutes or state that it can be submerged down below the water for centuries
So to summarize it all the 30minutes 1 meter is not the device limitation but just the certification's description.