This article recommends monthly asset reallocation with 10-20 weeks lookback. The methods was used for relatively slow indices during profoundly bull market. Probably the allocation frequency depends on market volatility, but should happen at least once a month for most markets.
Moreover, the same author mentions that it is best to reallocate at the end of each month. There is a known anomaly of higher returns in the first day of each month than any other day of the month, so probably this is justifying monthly rebalancing.
I quote:
A portfolio that is, at all times, invested 100% in either SPY or TLT. The switching, if necessary, is done monthly at the closing of the last trading day of the month. All the funds are invested in the instrument with the highest return over the previous 3 months. This portfolio is called “adaptive allocation”.