Bootstrap I.T. provide a range of support options.
The standard support contract (annual) includes email (24/7), phone/txt (office hours), fixed number of on-site visits per year, and online (Extended Office Hours).
Other options include 'incident-based' where all responses are charged on a minimum 15 minute period block, pre-purchased blocks of hours, and negotiated purpose-specific on-site visits.
Turn around time for responses are negotiated as part of a support contract, but as a minimum is guaranteed to be within 4 hours mon-fri.