SAP schedules minimal maintenance activities on the backbone systems which may result in the unavailability of the SAP support portal services, One support Launchpad ,SAP service marketplace etc.
Generally, SAP broadcasts a user message on the portal advising the users about the current maintenance activity in progress which might impact the users while accessing the support portal for searching SAP notes, opening the OSS connections, registering SAP licenses etc.
It gets really frustrating when you are in middle of a critical activity for which you need to apply a fix by implementing the SAP note or by referring the SAP KBAs for the resolution of the issues. Also, you cannot access the SAP incidents for raising the incidents with SAP.
Hence, it is recommended by SAP to plan your critical activities like upgrades or production maintenance activities such that they do not coincide with the SAP maintenance activities on the backbone systems as mentioned in SAP note 63945 .
SAP updates the note 63945 on regular basis and provides the schedule of the maintenance activities in advance. If your critical project is already planned and you cannot postpone the dates due to financial restrictions or business urgency, I would recommend that you download the latest versions of the SAP notes/guides for that activity in advance and have discussions with the SAP support representative for your companny in advance for the possibility of SAP support for very high priority incidents during maintenance activity.
You can also call the SAP hotline numbers in this note 63945 for the assistance