We offer instant help desk for our clients.  However, keep in mind that we are not a call center.  Instant help desk should only be offered as a solution to the client in the situation where the client needs help immediately and cannot wait as it is a business impacting priority.
A business impacting priority varies from client to client however some examples are below:
Cannot print and is in need to print due to Payroll or HR reasons
working from home and needs to connect to the office
More than 3 people within the business is impacted, down and or is unable to operate
Otherwise, you must always encourage the client that opening a ticket is the best solution and that a technician will be giving them a call back shortly.