随时 any time随地 any place随便 like you please (lit. as convenient=memory hook here)
Phonetic clue:
Sui-dynasty 隋
随 This character is not a compound of simpler characters, instead it is a rearrangement, simplification and mutation/corruption of other characters. The idea is: follow, submit to (the sui dynasty). It doesn’t appear to be part of any series, but a real weird character you must simply memorize as a stand-alone.