varnish vcl syntax

[X.H.R.F.C.]

Hello, 

Is there any way to get variable from regex and setup ttl ?

example:
application :

PHP
$this->response->headers(array('Content-Type' => 'text/html', 'esi-enabled' => 'true | 20m'));


VARNISH
if (beresp.http.esi-enabled ~ "true | [0-9a-z]+$") {
        set beresp.ttl = regsub(beresp.http.esi-enabled,"([0-9a-z]+$)","\0");
        unset beresp.http.esi-enabled;
}

after varnish restart i get:
Stopping HTTP accelerator: varnishd failed!
Starting HTTP accelerator: varnishd failed!
Message from VCC-compiler:
Expression has type STRING, expected DURATION

Regards
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