When playing triangle, tambourine and cymbal parts of the 18th, 19th and early 20th centuries – the exact duration of a note can often be unclear.
While composers of those periods were good at notating when to start a note, more often than not, they ignored indicating exactly how long to let a note resonate.
While there is no “rule of thumb”, a good way to approach this dilemma is to listen and match what is going on around you. Percussion parts often function to accentuate, or color the sound of other orchestral instruments. Use what you hear as a guide determining how long, or short, a note should be. If nothing else you will appear to be a musically sensitive player!