SR 4A p. 270
QUOTE
To learn or improve a skill or skill group, the character must succeed in an Extended Intuition + skill Test, with a threshold equal to the new skill rating x 2 and an interval of 1 week (1 month for skill groups). A teacher can add bonus dice to this test (see Using Instruction, p. 134).
the original printing had it a bit different
BBB p. 263
QUOTE
Learning Time: It is recommended that a character only be allowed to learn one new skill (or specialization, spell, or complex form) between adventures; the character cannot simultaneous improve any existing skills, attributes, etc. during this time. A character can be allowed to improve as many skills, attributes, etc. between adventures as she has Karma, assuming the gamemaster feels the improvement is warranted but each can only be improved once. If the time frame between adventures is longer than one month, gamemasters may increase these allowances as appropriate.
As for part 2 of the question I'd say make it an extended test BR "plumbing" or whatever interval of 1 hour and charge an hourly rate based on that. 150 nuyen/hour for a skilled tradesman would probably be about right.