Thank you all. Below code worked for me, the obstetrical I had was to convert String to datetime.
If you see in Line 3 even though I am eliminating Header and reading the date, the variable $myContent is storing some extra characters and thus when I try to convert, it throws an error. However I passed $myContent variable data into a text file and then read the content of text file into a separate variable $myVar and then applied datatype conversion on $myVar, which worked out here.
I am sure there would be much easy approaches, however this worked for me and unblocked me. Once again thank you all for your responses and support.
Line 1. [datetime]$whichDate = get-date
Line 2. [datetime]$myDate = ([datetime]$whichDate).AddDays(-1)
Line 3. $myContent = Get-EventLog -LogName System -Message “Kernel-Boot” -After $myDate -Newest 1 |select TimeGenerated |ft -HideTableHeaders
Line 4. $myContent |Out-File C:\MyFile.txt
Line 5. $myVar = Get-Content C:\MyFile.txt
Line 6. [datetime]$myTime = [datetime]::Parse("$myVar")