Merchandise orders (soft toys, books, clothing) are dispatched within 2-3 working days and can take up to 5 working days to be delivered in the UK, outside the UK this can be 14 working days.
If you ordered letters with merch, they wouldn't be sent together.
Letters are dispatched in the first week of the month. If you placed a subscription order in the first week of the month, your first letter would only be sent next month. Please see the postal dates for letters here. Delivery within the UK can take up to 5 working days and 14 days outside the UK.