Currently I have a members table with a lastvisit int(10) field.

When member's search for others members the results are ordered by lastvisit, eg:
select * FROM members ORDER BY lastvisit DESC

I'm introducing a new field, hiddentime, so member's can hide and be invisible to other members.

This works fine through out the site, except when it comes to ordering in search.
hiddentime is also an int(10) and set to 0 when not hidden. This stores the time they "go into hiding" and returns to "0" when they stop playing hide and seek.

I can not modify lastvisit as it is updated every page view, across many pages, plus the script is encoded in parts which makes that more trouble.

Is it possible to order by lastvisit but if they have a hiddentime to use the hiddentime instead of lastvisit time?

Thanks