Extracting timestamp in lua

edit

I am trying to extract the timestamp so I figure the following fields:

abs_time, utc_time, cls_time, rel_time

are containing the timestamp I need. Unfortunately, I got errors. According to Wireshark's official website:

https://www.wireshark.org/docs/wsdg_h...

One can extract those fields from the "pinfo" variable.

local function init_listener()
     local tap = Listener.new("ip",filter_packets)
     local ipid = Field.new("ip.id")
     function tap.reset()
         packets = 0;
     end
     function tap.packet(pinfo,tvb,ip)    
         -- as requested, double check with the previous code results. 

         -- tried this didn't worked.. 
         local val1 = pinfo.abs_time

         -- also want to extract those in the same manner .. 
         local val2 = pinfo.utc_time
         local val3 = pinfo.cls_time
         local val4 = pinfo.rel_time
         -- omitted
     end
     function tap.draw()
         print("Applying filter: " .. "\"" .. filter_packets .. "\"",packets)
     end
 end

So I have two questions :

1. Is it true that those fields hold the timestamp of a packet header?
2. How do I extract those fields in lua script?