The second observation is even more interesting if it is what I think it is. As far as I can tell, this is a party of slave raiding ants stealing larva from a neighboring ant colony! These are odd species of ants which steal larva from a different species of ant, then make them act as workers for the colony.
According to AntWiki:
Only a few raids have been observed, but from unpublished observations by Les Greenberg (U. C. Riverside, pers. comm.) and Geoff Trager (then a student at UC Santa Barbara, pers. comm.), we know that the raids take place in early to mid summer, in the latter half of the afternoon.Which exactly matches the timing I found these.