PowerShell Get-ADUser, output to JSON with formatted DateTime

I'll say first that I'm not very experienced with PowerShell, so many things are not obvious to me.

I've got the following command:

$JSON = Get-ADUser -Filter "SAMAccountName -eq 'jdray'" -Properties SAMAccountName,
    Name,
    DisplayName,
    Manager,
    SAMAccountType,
    pwdLastSet,
    Created,
    AccountExpirationDate,
    lastLogonTimestamp,
    DistinguishedName|Select-object -Property SAMAccountName,
                                    Name,
                                    @{name='Manager';expression={ ([ADSI]"LDAP://$($_.manager)").displayname }},
                                    Enabled,
                                    DistinguishedName,
                                    Created,
                                    AccountExpirationDate,
                                    LastLogonTimestamp,
                                    PasswordLastSet|ConvertTo-Json

The output of this is:

{
    "SAMAccountName":  "jdray",
    "Name":  "Ray, James",
    "Manager":  "Lady, Boss",
    "Enabled":  true,
    "DistinguishedName":  "CN=Ray\\, James,OU=...[yadda yadda yadda]...DC=com",
    "Created":  "\/Date(1554387070000)\/",
    "AccountExpirationDate":  "\/Date(1643702400000)\/",
    "LastLogonTimestamp":  132732539928955494,
    "pwdLastSet":  132729945927805005
}

First of all, I'm confused why AccountExpirationDate and Created have one format, but LastLogonTimestamp and pwdLastSet are formatted differently.

What I really want is to have all the DateTime objects output in a human-readable DateTime format. I tried -ExpandProperty, but couldn't figure out how to make it work. It appears to add a property named DateTime to the end of the output, formatted reasonably: "DateTime": "Thursday, April 4, 2019 7:11:10 AM", but it doesn't name it. The Microsoft documentation on the subject is very light on useful examples, as is the rest of the web.

I tried following the @{} format for the Manager expression, which I copied from someone else's script. Unfortunately my PowerShell isn't strong enough to figure out a reasonable expression. In C#, something like Created.ToShortDateString() would suffice (presuming Created is a DateTime).

So, how do I consistently output named, human-readable DateTime property values in a JSON array?

EDIT

Using a proposed answer below, I modified the four timestamp fields using the same pattern:

@{n='Created';e={[DateTime]::FromFileTime($_.Created)}},
@{n='AccountExpirationDate';e={[DateTime]::FromFileTime($_.AccountExpirationDate)}},
@{n='LastLogonTimestamp';e={[DateTime]::FromFileTime($_.lastLogonTimestamp)}},
@{n='pwdLastSet';e={[DateTime]::FromFileTime($_.pwdLastSet)}}

Here's the (frustrating) result I got:

 "Created":  "\/Date(1554387070000)\/",
 "AccountExpirationDate":  "\/Date(1643702400000)\/",
 "LastLogon":  {
                   "value":  "\/Date(1628780392895)\/",
                   "DateTime":  "Thursday, August 12, 2021 7:59:52 AM"
               },
 "pwdLastSet":  132729945927805005

Also of note, here's the output for the four DateTime fields before it gets translated to JSON:

Created               : 4/4/2019 7:11:10 AM
AccountExpirationDate : 2/1/2022 12:00:00 AM
LastLogonTimestamp    : 8/12/2021 7:59:52 AM
PasswordLastSet       : 8/9/2021 7:56:32 AM

Why does that formatting work for one DateTime instance but not the rest?

How do I extract DateTime from the format of the pwdLastSet field, which is clearly a different animal?

How do I get a simple property:value pair, such as "LastLogonTimestamp": "Thursday, August 12, 2021 7:59:52 AM"?