Yes, you can use It's deductible all year long, you can track donations for 2018 as well as any previous years donations that you may have missed. Please see the screenshot here: https://gyazo.com/6e94e147486f368112805e9741fb1f6c
Here is the link for It's Deductible for easy access: https://itsdeductibleonline.intuit.com/secured/LoginHome.htm
As a suggestion, if you make donations frequently, you can save this link to your browser favorites.