Although John Muller has confirmed that no PageRank(RIP) is lost, Moz has claimed that there is some studies that confirmed the contrary. Either way, in my opinion, it is safer to assume that some “link juice” is lost.
The delay won’t really matters because clients wait for the server response and then fetch response content. 301 will be the response, In which case “link flow” will not be disrupted. Technically in the SEO world this is not worth trying, even if you want to deceive Google.
After Question Clarification
If the content stays the same between the old and the new domain, I would recommend to leave the content up, take advantage of well supported cross-domain canocalisation and create a canonical tag making reference to the new domain. I would also create a Pop-Up window or a top sliding window message to display a notification text with a link to the new page/domain. Then, wait until Google Index the new domain or De-Index the old domain entirely, and implement the 301.