Freelancer.com seems to avoid deliberately stating how their bid ranking algorithms work, but they do provide a bid ranking guide, written by Emma D, that gives you a set of tips to increase your chances of interacting with the employer. The very first tip they present is, with my emphasis on the important part:
Bid Early: Can’t get to the top? Bid before the others do. Early bidders consistently win more projects since it increases their chances of interacting with the employer.
Couple this with the anecdotal experience you have with your late bids being ranked lower, and I think that we can safely say that early bidders do in fact get a boost to their bid's rank. Even if they don't, the increase in visibility granted to those who bid early is very certainly worth it.
There is a sort by bid time function, but it's not so important.
The first thing I said is most important reason. – Sato Takeru Oct 09 '21 at 12:45