It's a Small World Holiday will usually close for the removal of the overlay sometime in mid-to-late January (usually right around or right after MLK Day), and it should take about 2 or 2-1/2 weeks before it reopens. It will be open at least through January 17th (that's how far the
Disneyland calendar extends right now).
Haunted Mansion Holiday
usually closes immediately after the last day of the holiday season (which will be 1/6/15), and reopens before IASWH closes (so that they are not both closed at the same time).
However, this time around the DLR calendar is showing Haunted Mansion Holiday as being open through Sunday, January 11, 2015 and being closed on Monday, 1/12/15. I don't know if this change in schedule is correct, or if it is due to the expected mobs of people who will be descending on DLR that week to see the new Frozen Fun events in DL and DCA.
It takes about 10 days to 2 weeks to get the HM back to its regular version. Our competitor site -- Mouse Planet -- at one point reported that HMH would be closed from Monday, 1/12/15 - Thursday, 1/22/15. I don't know if that is accurate, but if it is then I would expect It's a Small World Holiday to close down for overlay removal sometime between Friday, 1/23/15 and Monday, 1/26/15 (and then be down for 2 weeks or so), so the two ride closures don't overlap, but we'll see....