Once the client receives the link, they should put time aside to work through all the questions in all the sections in one go.
If they stop, shut down the window and come back after completing some of the questions, the answers will not be saved so the client will have to start from scratch.
The link stays active until it is fully completed by the client and then becomes inactive.
Clients will be able to complete the questionnaire on a mobile device, it will not be perfect but it is doable.