Well, only if your UI allows dragging two items at once. If you reorder multiple items, well, I suppose you can resolve it by passing some relative position. If you want to squeeze something in-between reordered items, then -1 probably is not a good choice, but more like calculating some middle value between previous and next item.
What would the timestamp represent? Are you providing a timestamp which encodes the position somehow, or using CURRENT_TIMESTAMP? Updating the timestamp for all of the rows in the (sub) list? How does this permit you to reorder the items in the list?
Timestamp would only represent position and enables to put something in between, rather than an integer which adds +1. If put A (timestamp = 100) between B (timestamp = 200) and C (timestamp = 300), just set that order value to middle (150). Naive
It actually looks the same as "What about leaving room?" and, yeah, introduces complexity when you organize items for too long.
