This was our timeline for a Transit Visa.
Applied online through IRCC website: 24 April
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Request to submit passport for stamping: 15 May
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Submitted passport in person at VFS London: 16 May, 10 am (you have to submit before 10:30 am in order for the passport to be dispatched to the embassy on the same day).
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IRCC online account updated with stamped visa counterfoil details: 21 May
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Passport dispatched to VFS London: 22 May
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Passport with stamped visa counterfoil collected in person: 22 May, 4 pm
Visa issued was a VH1 category visitor visa with two entries and validity of 6 months.
Time from submission of application to request for passport was 21 days, which was slightly more than the estimated processing time of 18 days when we applied.
Time from submission of passport at VFS to collection at VFS was 4 business days, including date of submission and collection. This is the minimum time for stamping, as we were advised by VFS.
If you are posting applications, add at least 2 business days each for sending and receiving the passport.
Hope this is helpful. Please apply well in advance because this was very stressful. We literally received the passport back at the 11th hour before travel!