There's a regular working Monday to Wednesday nights as part of the track renewal works between Baker Street and Finchley Road - the train will sit at Finchley Road and then Baker Street (usually platform 4, but not always) until access to the possession is granted after the last Met line trains have cleared the section. The early closure commences c2130 so it's a good opportunity to 'spot' a train without staying out to close of traffic.
Otherwise, your best option is on the Met between Ruislip and Rayners Lane from around 2330 Sunday-Thursday. There's usually at least one train out every night, but the time is flexible depending how far it has to operate. At weekends when there are large engineering (as opposed to testing, such as many of the current ones on the SSL) shutdowns there will be a lot more trains in an evening.
Daylight runs are rare but not unheard of - generally adhoc to get to and from weekend possessions but sometimes - particularly in the summer - there are other options when things like the weedkilling trains run.
The times themselves are wildly subject to change and variation for all trains, and unless you have a driver's radio number you can't guarantee it will necessarily do what it is supposed to on paper. HTH.
