How to resolve error "String not recognized as valid DateTime"? - powershell-4.0

Question

I have three date type variables passed from a batch file as strings. When they come over to the PS script, they are seen as:
20190710 112538
20190710 112538
20190710
The problem I am facing is that when I attempt to parse them, I receive an error stating that the string is not recognized as a valid DateTime.
I have tried changing the culture to and invariant one and no difference. I am sure I am missing something. Could I get some help with parsing these strings successfully?
Values Sent from here:
set YYYY=%DATE:~-4%
set MM=%DATE:~4,2%
set DD=%DATE:~7,2%
set HH=%time:~0,2%
set NN=%time:~3,2%
set SS=%time:~6,2%
set MS=%time:~9,2%
SET "_oStart=%YYYY%%MM%%DD% %HH%%NN%%SS%%MS%"
SET "_PSScript=C:\xx\xx.ps1"
SET "_oEnd=%YYYY%%MM%%DD% %HH%%NN%%SS%%MS%"
SET "_oDateRan=%YYYY%%MM%%DD%"
SET "_PSCMD=Powershell -ExecutionPolicy Bypass -File "%_PSScript%" -oStart "%_oStart%" -oEnd "%_oEnd%" -oDateRan "%_oDateRan%"
Param(
[String]$oStart,
[String]$oEnd,
[String]$oDateRan
)
[DateTime]$DateRan = [DateTime]::ParseExact($oDateRan, "yyyyMMdd", $null)
[DateTime]$StartTime = [DateTime]::ParseExact($oStart, "yyyyMMdd HHmmssff", $null)
[DateTime]$End = [DateTime]::ParseExact($oEnd, "yyyyMMdd HHmmssff", $null)
Error Message:
Exception calling "ParseExact" with "3" argument(s): "String was not
recognized as a valid DateTime."