LHR-YVR-YYC on BA/WS: Advice Sought: OSS, ITD and MCT

Hi,

Booked on BA from LHR to YVR connecting to WS to YYC, all on one ticket, one PNR.

Do I qualify for OSS?
How about ITD?

There is a schedule change on WS so I might be able to request BA to put me on earlier WS flight for YVR YYC.

What is the MCT for my set of flights? And what is the minimum layover I should be practically booking on? I might mention here that upon doing a fresh search on ba.com, flights with 1h35min separation at YVR do not appear in the search results but 2h35min, 3h35min and 4h35min separation show up. Is it a risk requesting them for 1h35 min connection if they allow?

Thanks a lot in advance!

Regards
Vik