Measured tafl game lengths.

Tafl variant	All games moves	White won moves	Black won moves	Ratio
Market Hnefatafl 9x9	33	31	35	1.1
Simple Hnefatafl 11x11 (aka Welsh Tawlbwrdd)	33	30	37	1.2
Historical Hnefatafl 9x9 (aka Saami Tablut)	39	33	45	1.4
Historical Hnefatafl 11x11	44	38	50	1.3
Historical Hnefatafl 13x13	54	41	66	1.6
Total Hnefatafl 11x11	62	48	75	1.6
Copenhagen Hnefatafl 11x11	64	49	78	1.6
Alea Berserk 19x19 (Bartley)	84	72	98	1.3
Frisian Dablo0 11x9	50	49	51	1.0
Frisian Dablo 11x9	73	69	76	1.1
Saami Daabloe 11x9	81	80	83	1.0
Saami Sahkku 3x15 (Kaafjord)	43	44	43	1.0
Daldos 3x12	40	40	40	1.0
Daldos 3x14	49	49	49	1.0
Daldos 3x16	43	42	43	1.0

The table shows for each game variant the quadratic average of the number of moves for all games, for games alone where defenders (white) won and games alone where attackers (black) won.

Some of the variants come out very steady, in that it almost doesn't matter to the gamelength whether white or black wins.
Such variants are suited for use of a chess clock.