I would agitate constantly in a tray, but I've never had streaking problems. You can see it happening if you use a white tray and have good light, but for reference, I usually go about 8 minutes in Kodak RST 1:3, 68 deg. for thoroughly washed negs (re-wet them first, if they are dry) that have been fixed in an acid fixer. I haven't timed it precisely for negs fixed in TF-4, but it's probably shorter.