In one of Dalinars visions he talks to Nohodon, and he says that not all spren are as picky with the ideals as Honorspren. In WoR after he accidentally swears himself into a corner Oath wise the stormlight is less effective than before, so Syl could be "promoting" him by allowing more access to stormlight. Pattern also talks about reviving broken spren, I imagine the process is different than what Kaladin dod as Syl wasnt truely dead, just gone. However that could account for the delay. Its also worth noting that Dalinar didnt get any Shards and the Bondsmiths are noted as being drastically different from the other Orders in Words of Radiance WoR the book Jasnah gave Shallan. There being only 3 members at any one time.
I infer that the Nightwatcher is the same as the Stormfather, a spren of one of the Shards, in her case Cultivation. Her boons fit with Cultivating, pruning and planting and such, give and take. Dalinar bonding the Stormfather gives a possible reason for there only ever being three of them. Three shards, three shard-spren, three bondsmiths bound to them.