That would be the level of information expected from a pointy-hair boss. There are various software development / maintenance estimation algorithms e.g. COCOMO. It would depend on what volume of work you mean by 'update'. What are you starting with and what constitutes completion.
Experience or metrics would also help with estimation (see QA), but whatever you decide make sure you measure the actual effort and use it to estimate your next 'update'
Hi, Perhapse u can desing ur own Estimation sheet . Just break whole script into bricks/pieces of which they are made of (Like OR-objects,functions,actions, actions etc.)
Allot some unit time req to update them, (like 10min to add a new object into OR, 30 mins 2 write and unit test a new medium size function etc. )
Now when ever u hv to update a new script , just estimate how mach chnge it will cause and then calulate the approximate time requiered to do it.