If you attended post secondary school for 5 months, it would convert to 20 weeks on the T778.
When using TurboTax Standard, the T2202A does require you to enter in months as opposed to weeks. Please see the attached screenshot for clarification.
I switched to Chrome and it's still saying the same thing under CHILD CARE EXPENSES INTRO, which is:
Did you attend school in 2018?
Complete the following if, at any time in 2018, you were enrolled in an educational program.
Number of full months you attended school part-time only
Number of full weeks you attended school full-time
As you can see by the attached screenshot (I've also included a link to the CRA form), CRA clearly requires weeks for the childcare section. If you would like to view the form used to calculate tuition credits (for which your T2202A is used), I'll be happy to provide that as well. Please see the screenshot and the following link. https://www.canada.ca/content/dam/cra-arc/formspubs/pbg/t778/t778-18e.pdf