gistfile1.ps1

function Convert-TimeStringToTimeSpan($TimeString) {
    $AllowedLabels = (New-TimeSpan).Psobject.Properties.Name
    ## Add the singular values as well
    $AllowedLabels += $AllowedLabels | foreach { $_.TrimEnd('s') }
    ## Strip the 'for' string
    $TimeString = $TimeString.TrimStart('for ')
    ## Attempt to split on the 'and' string in case it was something like 1 hour and 15 minutes
    $Values = $TimeString -split ' and '
    
    $Hours = 0
    foreach ($Value in $Values) {
        $Split = $Value.Split(' ')
        $Value = $Split[0]
        if ($AllowedLabels -notcontains $Label) {
            Write-Error "The label '$Label' is not a valid time label"
            return $false
        } elseif ($Value -notmatch '^\d+$') {
            Write-Error "The time value '$Value' is not a valid time interval"
            return $false
        } else {
            $Label = $Split[1]
            ## Make the label plural (if it's not already) to match New-TimeSpan's property name
            if ($Label.Substring($Label.Length - 1, 1) -ne 's') {
                $Label = $Label + 's'
            }
            Write-Verbose "Passing the label $Label and value $Value to New-TimeSpan"
            ## Convert the time to hours
            $Params = @{ $Label = $Value }
            $Hours += (New-TimeSpan @Params).TotalHours
        }
    }
    [math]::Round($Hours,2)
}

Convert-TimeStringToTimeSpan -TimeString '1 day and 3600 seconds'
Convert-TimeStringToTimeSpan -TimeString '45 days and 5 hours'