Complex sentence: Such times can prove fruitful for spiritual progress, as external constraints diminish, although they offer challenges because our unskillful impulses can come to the fore, just as in the "sidpa bardo".
Split into simpler sentences: Such times can prove fruitful for spiritual progress because external constraints diminish. However, they can also present challenges because our less skillful impulses may come into the foreground, just as in the "sidpa bardo".