Hope4bb,
2 years back when I first failed my fresh ccycle, I rested 2m before doing FET It depends on how ready uare. If u feel u can do it the next cycle, u can proceed. There's no hard and fast rules as to when can start.
For mine, I did natural FET, my doc scan and monitor my egg growth and when nearer to ovulation date, she help me do BT to check hormones and ovulation. When ovulated, they gave me a jab and 2 days later can do the ET le.
As for medicated, need to let the other sisters here to tell u. But I guess its more or less the same but for medicated, they use jabs to control the whole cycle.