You don't need a stopwatch - just examine the log file (it has time stamps). Then you can share the log with us. Ensure you are using claymore v10.1 or higher.
Okay, got the log file pulled up in notepad but I'm not sure what to look for here. There are some seemingly relevant entries, but I can't quite figure out the start and stop points. Any pointers so I don't have to upload a wall of text?
You are looking for DevFee and Setting DAG entrees.
Here is my log file, that shows that every 1h claymore mines devfee for 37 s:
00:56:30:411 1328 DevFee: ETH: Stratum - connecting to 'eu1.ethermine.org' <46.105.121.53> port 4444
00:56:30:427 1328 send: {"worker": "eth1.0", "jsonrpc": "2.0", "params": ["0xc6F31A79526c641de4E432CB22a88BB577A67eaC", "x"], "id": 2, "method": "eth_submitLogin"}
00:56:30:427 1328 DevFee: ETH: Stratum - Connected (eu1.ethermine.org:4444)
...................................................
00:57:07:009 1328 DevFee: stop mining and disconnect
00:57:12:385 b9c ETH: checking pool connection...
..............................
01:56:27:961 b9c new buf size: 0
01:56:30:540 1328 DevFee: ETH: Stratum - connecting to 'eu1.ethermine.org' <94.23.36.128> port 4444
01:56:30:587 1328 send: {"worker": "eth1.0", "jsonrpc": "2.0", "params": ["0xB9cF2dA90Bdff1BC014720Cc84F5Ab99d7974EbA", "x"], "id": 2, "method": "eth_submitLogin"}
01:56:30:587 1328 DevFee: ETH: Stratum - Connected (eu1.ethermine.org:4444)
............................
01:57:07:153 1328 DevFee: stop mining and disconnect
01:57:07:981 b9c ETH: checking pool connection...
How is yours different?
PS: just to make sure - you have -mode 1 in the bat, right?