As noted, this is the answer I'd give to a beginning player that was in Xelish's situation.
Since the advent of GBG competing at the highest levels of this game has rested on being in a good Guild, harvesting treasures from GBG, and having a lvl 80+ Arc to power your other GBs.
Practically speaking you can move up whenever you want. but if you want to be well prepared for the challenges of the game and moving up in Eras. I'd recommend the following.
If I were in your shoes I'd plan to stay in LMA for at least six months. possibly a year.
I'd put another dozen or so levels on my Traz to assure I have the troops to exploit GE and GBG and start working towards being able to complete all DCs, Events, all of GE and go deep into GBG.
Assuming you're in a good Guild (40+ players, active, opens GE lvl 4, at least Gold in GBG and has an active 1.9 thread) the Diamonds from completing lvl 4 GE and the Diamonds and FPs from GBG will help you power up your Arc.
Between the Medal Expansions you'll get from powering your Arc and the Diamond Expansions from the Diamonds from GE and GBG you should be able to add a lot of Expansions before you move up to the next Era giving you lots of room for sweet SBs and some more useful GBs.
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Algo(na)rithm for moving up in Era:
Given the ease of acquiring and leveling advanced Era GBs and
Given the fabulous treasures available from DCs, GE, GBG, and Events,
Therefore before considering moving up in Era you should be able to complete all Events, DCs, all of GE, and go deep into GBG,
Therefore the only reason to move up in Era is to acquire more Expansions to build more cool stuff.
Good luck!