I should warn in advance that this data was done without including packs and EU - all the number crushing is turned towards the F2P aspect of the goal. It was done duing the one-day event "Magical Melee", where the 8* had a 15k Spell Stones requirement
The last time that i had Legend was when i did 6 1-CP battles which triggered it, and 8 3-CP battles with 4 free tonics. Those eight battles took roughly half the Legend time, which meant that one full timer, if "sprinting" correctly, will use 24 TE over 15 minutes. So a plausible outcome would be that one could do a full Legend cycle over 20 to 30 minutes, using between 30 and 35 TE.
Those 8 minutes yielded 350 stones, plus 100 from a lucky gold chest found on rook battles. Considering such, a statistically valid shard generation would be 700-900 in said Legend cycle. therefore, a F2P player could win roughly 1400 - 2700 stones over an hour of non-stop gameplay. Considering the TE used, the value could change from 40 to 90 stones per TE. This value does prove that is advisable to purchase the daily tonics at 50 stones each, giving a potential gain of 70 to 220 stones per tonic.
To reach Lamora, considering the above calculations, one would need between 5 hours 34 minutes and 10 hours 42 minutes to reach her, using between 167 and 375 TE.
Since Lamora is placed at a higher rate than previous completion rewards, as Maya and Rakel both required 10k per day on previous events, one might suggest a goal of 112 to 250 TE per day over every 8-10 hours of daily gameplay to reach a completion Clash 8* with a requirement of 10k shards per day.