The term Input service has been defined under rule (l) of CENVAT Credit rules, 2004 which is reproduced below for ease of reference.
(l) "input service" means any service,-
(i) used by a provider of taxable service for providing an output service; or
(ii) used by the manufacturer, whether directly or indirectly, in or in relation to the manufacture of final products and clearance of final products from the place of removal,
and includes services used in relation to setting up, modernization, renovation or repairs of a factory, premises of provider of output service or an office relating to such factory or premises, advertisement or sales promotion, market research, storage upto the place of removal, procurement of inputs, activities relating to business, such as accounting, auditing, financing, recruitment and quality control, coaching and training, computer networking, credit rating, share registry, and security, inward transportation of inputs or capital goods and outward transportation upto the place of removal;
As per this the services relating to accounting and auditing are also treated as input service. Hence you can take credit of service tax on such input services.
Answer to your second question is that it can be taken as soon as possible. There is no time limit specified and hence the credit may be taken in the next financial year. As a word of caution, the terms used in the act and rules are credit availing and credit utilizing. Therefore the CENVAT credit may be availed and utilized at the earliest.