On this 1914 isochronic map, the journey time to China is shown as '20 to 30 days':
https://www.dailymail.co.uk/sciencetech/article-3339902/What-travel-looked-like-100-years-ago-Map-shows-DAYS-took-travel-abroad-1900s.html
I doubt that there would have been significant changes in journey times over the preceding 15 years. So, putting that together with Dee-M-See's post, a guideline time of 'about a month' might be a reasonable estimate. (The actual journey time would have depended upon the characteristics of the particular class of ship used and other factors too, such as the number of port calls en route to load and unload cargo).
Your grandfather will have got there a lot quicker than his predecessors did though, before the days of steam. 'The Witch of the Wave' (an American clipper) sailed from Canton to Deal in 1852 in what was then regarded as an astoundingly fast journey time of 90 days.