I'm assuming you searched CPAN and noone made a portable solution. That means you'll need to get the info from the system, but you didn't specify your OS.

That said, I'm also very curious as to why you need the start time of some arbitrary process.

Update: Hum, you didn't look on CPAN, I'd say. In a few seconds, I found

• Win32::Process::Info
• Win32::Process::Info::NT
• Win32::Process::Info::PT
• Win32::Process::Info::WMI
• BSD::Process
• Sys::Statistics::Linux::Processes
• Proc::ProcessTable
• Surely more!

The last even appears to be a portable solution!